[perl5.git] / toke.c

/*    toke.c
 *
 *    Copyright (C) 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
 *    2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008 by Larry Wall and others
 *
 *    You may distribute under the terms of either the GNU General Public
 *    License or the Artistic License, as specified in the README file.
 *
 */

/*
 *  'It all comes from here, the stench and the peril.'    --Frodo
 *
 *     [p.719 of _The Lord of the Rings_, IV/ix: "Shelob's Lair"]
 */

/*
 * This file is the lexer for Perl.  It's closely linked to the
 * parser, perly.y.
 *
 * The main routine is yylex(), which returns the next token.
 */

/*
=head1 Lexer interface

This is the lower layer of the Perl parser, managing characters and tokens.

=for apidoc AmU|yy_parser *|PL_parser

Pointer to a structure encapsulating the state of the parsing operation
currently in progress.  The pointer can be locally changed to perform
a nested parse without interfering with the state of an outer parse.
Individual members of C<PL_parser> have their own documentation.

=cut
*/

#include "EXTERN.h"
#define PERL_IN_TOKE_C
#include "perl.h"
#include "dquote_static.c"

#define new_constant(a,b,c,d,e,f,g)     \
        S_new_constant(aTHX_ a,b,STR_WITH_LEN(c),d,e,f, g)

#define pl_yylval       (PL_parser->yylval)

/* XXX temporary backwards compatibility */
#define PL_lex_brackets         (PL_parser->lex_brackets)
#define PL_lex_allbrackets      (PL_parser->lex_allbrackets)
#define PL_lex_fakeeof          (PL_parser->lex_fakeeof)
#define PL_lex_brackstack       (PL_parser->lex_brackstack)
#define PL_lex_casemods         (PL_parser->lex_casemods)
#define PL_lex_casestack        (PL_parser->lex_casestack)
#define PL_lex_defer            (PL_parser->lex_defer)
#define PL_lex_dojoin           (PL_parser->lex_dojoin)
#define PL_lex_expect           (PL_parser->lex_expect)
#define PL_lex_formbrack        (PL_parser->lex_formbrack)
#define PL_lex_inpat            (PL_parser->lex_inpat)
#define PL_lex_inwhat           (PL_parser->lex_inwhat)
#define PL_lex_op               (PL_parser->lex_op)
#define PL_lex_repl             (PL_parser->lex_repl)
#define PL_lex_starts           (PL_parser->lex_starts)
#define PL_lex_stuff            (PL_parser->lex_stuff)
#define PL_multi_start          (PL_parser->multi_start)
#define PL_multi_open           (PL_parser->multi_open)
#define PL_multi_close          (PL_parser->multi_close)
#define PL_pending_ident        (PL_parser->pending_ident)
#define PL_preambled            (PL_parser->preambled)
#define PL_sublex_info          (PL_parser->sublex_info)
#define PL_linestr              (PL_parser->linestr)
#define PL_expect               (PL_parser->expect)
#define PL_copline              (PL_parser->copline)
#define PL_bufptr               (PL_parser->bufptr)
#define PL_oldbufptr            (PL_parser->oldbufptr)
#define PL_oldoldbufptr         (PL_parser->oldoldbufptr)
#define PL_linestart            (PL_parser->linestart)
#define PL_bufend               (PL_parser->bufend)
#define PL_last_uni             (PL_parser->last_uni)
#define PL_last_lop             (PL_parser->last_lop)
#define PL_last_lop_op          (PL_parser->last_lop_op)
#define PL_lex_state            (PL_parser->lex_state)
#define PL_rsfp                 (PL_parser->rsfp)
#define PL_rsfp_filters         (PL_parser->rsfp_filters)
#define PL_in_my                (PL_parser->in_my)
#define PL_in_my_stash          (PL_parser->in_my_stash)
#define PL_tokenbuf             (PL_parser->tokenbuf)
#define PL_multi_end            (PL_parser->multi_end)
#define PL_error_count          (PL_parser->error_count)

#ifdef PERL_MAD
#  define PL_endwhite           (PL_parser->endwhite)
#  define PL_faketokens         (PL_parser->faketokens)
#  define PL_lasttoke           (PL_parser->lasttoke)
#  define PL_nextwhite          (PL_parser->nextwhite)
#  define PL_realtokenstart     (PL_parser->realtokenstart)
#  define PL_skipwhite          (PL_parser->skipwhite)
#  define PL_thisclose          (PL_parser->thisclose)
#  define PL_thismad            (PL_parser->thismad)
#  define PL_thisopen           (PL_parser->thisopen)
#  define PL_thisstuff          (PL_parser->thisstuff)
#  define PL_thistoken          (PL_parser->thistoken)
#  define PL_thiswhite          (PL_parser->thiswhite)
#  define PL_thiswhite          (PL_parser->thiswhite)
#  define PL_nexttoke           (PL_parser->nexttoke)
#  define PL_curforce           (PL_parser->curforce)
#else
#  define PL_nexttoke           (PL_parser->nexttoke)
#  define PL_nexttype           (PL_parser->nexttype)
#  define PL_nextval            (PL_parser->nextval)
#endif

/* This can't be done with embed.fnc, because struct yy_parser contains a
   member named pending_ident, which clashes with the generated #define  */
static int
S_pending_ident(pTHX);

static const char ident_too_long[] = "Identifier too long";

#ifdef PERL_MAD
#  define CURMAD(slot,sv) if (PL_madskills) { curmad(slot,sv); sv = 0; }
#  define NEXTVAL_NEXTTOKE PL_nexttoke[PL_curforce].next_val
#else
#  define CURMAD(slot,sv)
#  define NEXTVAL_NEXTTOKE PL_nextval[PL_nexttoke]
#endif

#define XENUMMASK  0x3f
#define XFAKEEOF   0x40
#define XFAKEBRACK 0x80

#ifdef USE_UTF8_SCRIPTS
#   define UTF (!IN_BYTES)
#else
#   define UTF ((PL_linestr && DO_UTF8(PL_linestr)) || ( !(PL_parser->lex_flags & LEX_IGNORE_UTF8_HINTS) && (PL_hints & HINT_UTF8)))
#endif

/* The maximum number of characters preceding the unrecognized one to display */
#define UNRECOGNIZED_PRECEDE_COUNT 10

/* In variables named $^X, these are the legal values for X.
 * 1999-02-27 mjd-perl-patch@plover.com */
#define isCONTROLVAR(x) (isUPPER(x) || strchr("[\\]^_?", (x)))

#define SPACE_OR_TAB(c) ((c)==' '||(c)=='\t')

/* LEX_* are values for PL_lex_state, the state of the lexer.
 * They are arranged oddly so that the guard on the switch statement
 * can get by with a single comparison (if the compiler is smart enough).
 *
 * These values refer to the various states within a sublex parse,
 * i.e. within a double quotish string
 */

/* #define LEX_NOTPARSING               11 is done in perl.h. */

#define LEX_NORMAL              10 /* normal code (ie not within "...")     */
#define LEX_INTERPNORMAL         9 /* code within a string, eg "$foo[$x+1]" */
#define LEX_INTERPCASEMOD        8 /* expecting a \U, \Q or \E etc          */
#define LEX_INTERPPUSH           7 /* starting a new sublex parse level     */
#define LEX_INTERPSTART          6 /* expecting the start of a $var         */

                                   /* at end of code, eg "$x" followed by:  */
#define LEX_INTERPEND            5 /* ... eg not one of [, { or ->          */
#define LEX_INTERPENDMAYBE       4 /* ... eg one of [, { or ->              */

#define LEX_INTERPCONCAT         3 /* expecting anything, eg at start of
                                        string or after \E, $foo, etc       */
#define LEX_INTERPCONST          2 /* NOT USED */
#define LEX_FORMLINE             1 /* expecting a format line               */
#define LEX_KNOWNEXT             0 /* next token known; just return it      */


#ifdef DEBUGGING
static const char* const lex_state_names[] = {
    "KNOWNEXT",
    "FORMLINE",
    "INTERPCONST",
    "INTERPCONCAT",
    "INTERPENDMAYBE",
    "INTERPEND",
    "INTERPSTART",
    "INTERPPUSH",
    "INTERPCASEMOD",
    "INTERPNORMAL",
    "NORMAL"
};
#endif

#ifdef ff_next
#undef ff_next
#endif

#include "keywords.h"

/* CLINE is a macro that ensures PL_copline has a sane value */

#ifdef CLINE
#undef CLINE
#endif
#define CLINE (PL_copline = (CopLINE(PL_curcop) < PL_copline ? CopLINE(PL_curcop) : PL_copline))

#ifdef PERL_MAD
#  define SKIPSPACE0(s) skipspace0(s)
#  define SKIPSPACE1(s) skipspace1(s)
#  define SKIPSPACE2(s,tsv) skipspace2(s,&tsv)
#  define PEEKSPACE(s) skipspace2(s,0)
#else
#  define SKIPSPACE0(s) skipspace(s)
#  define SKIPSPACE1(s) skipspace(s)
#  define SKIPSPACE2(s,tsv) skipspace(s)
#  define PEEKSPACE(s) skipspace(s)
#endif

/*
 * Convenience functions to return different tokens and prime the
 * lexer for the next token.  They all take an argument.
 *
 * TOKEN        : generic token (used for '(', DOLSHARP, etc)
 * OPERATOR     : generic operator
 * AOPERATOR    : assignment operator
 * PREBLOCK     : beginning the block after an if, while, foreach, ...
 * PRETERMBLOCK : beginning a non-code-defining {} block (eg, hash ref)
 * PREREF       : *EXPR where EXPR is not a simple identifier
 * TERM         : expression term
 * LOOPX        : loop exiting command (goto, last, dump, etc)
 * FTST         : file test operator
 * FUN0         : zero-argument function
 * FUN0OP       : zero-argument function, with its op created in this file
 * FUN1         : not used, except for not, which isn't a UNIOP
 * BOop         : bitwise or or xor
 * BAop         : bitwise and
 * SHop         : shift operator
 * PWop         : power operator
 * PMop         : pattern-matching operator
 * Aop          : addition-level operator
 * Mop          : multiplication-level operator
 * Eop          : equality-testing operator
 * Rop          : relational operator <= != gt
 *
 * Also see LOP and lop() below.
 */

#ifdef DEBUGGING /* Serve -DT. */
#   define REPORT(retval) tokereport((I32)retval, &pl_yylval)
#else
#   define REPORT(retval) (retval)
#endif

#define TOKEN(retval) return ( PL_bufptr = s, REPORT(retval))
#define OPERATOR(retval) return (PL_expect = XTERM, PL_bufptr = s, REPORT(retval))
#define AOPERATOR(retval) return ao((PL_expect = XTERM, PL_bufptr = s, REPORT(retval)))
#define PREBLOCK(retval) return (PL_expect = XBLOCK,PL_bufptr = s, REPORT(retval))
#define PRETERMBLOCK(retval) return (PL_expect = XTERMBLOCK,PL_bufptr = s, REPORT(retval))
#define PREREF(retval) return (PL_expect = XREF,PL_bufptr = s, REPORT(retval))
#define TERM(retval) return (CLINE, PL_expect = XOPERATOR, PL_bufptr = s, REPORT(retval))
#define LOOPX(f) return (pl_yylval.ival=f, PL_expect=XTERM, PL_bufptr=s, REPORT((int)LOOPEX))
#define FTST(f)  return (pl_yylval.ival=f, PL_expect=XTERMORDORDOR, PL_bufptr=s, REPORT((int)UNIOP))
#define FUN0(f)  return (pl_yylval.ival=f, PL_expect=XOPERATOR, PL_bufptr=s, REPORT((int)FUNC0))
#define FUN0OP(f)  return (pl_yylval.opval=f, CLINE, PL_expect=XOPERATOR, PL_bufptr=s, REPORT((int)FUNC0OP))
#define FUN1(f)  return (pl_yylval.ival=f, PL_expect=XOPERATOR, PL_bufptr=s, REPORT((int)FUNC1))
#define BOop(f)  return ao((pl_yylval.ival=f, PL_expect=XTERM, PL_bufptr=s, REPORT((int)BITOROP)))
#define BAop(f)  return ao((pl_yylval.ival=f, PL_expect=XTERM, PL_bufptr=s, REPORT((int)BITANDOP)))
#define SHop(f)  return ao((pl_yylval.ival=f, PL_expect=XTERM, PL_bufptr=s, REPORT((int)SHIFTOP)))
#define PWop(f)  return ao((pl_yylval.ival=f, PL_expect=XTERM, PL_bufptr=s, REPORT((int)POWOP)))
#define PMop(f)  return(pl_yylval.ival=f, PL_expect=XTERM, PL_bufptr=s, REPORT((int)MATCHOP))
#define Aop(f)   return ao((pl_yylval.ival=f, PL_expect=XTERM, PL_bufptr=s, REPORT((int)ADDOP)))
#define Mop(f)   return ao((pl_yylval.ival=f, PL_expect=XTERM, PL_bufptr=s, REPORT((int)MULOP)))
#define Eop(f)   return (pl_yylval.ival=f, PL_expect=XTERM, PL_bufptr=s, REPORT((int)EQOP))
#define Rop(f)   return (pl_yylval.ival=f, PL_expect=XTERM, PL_bufptr=s, REPORT((int)RELOP))

/* This bit of chicanery makes a unary function followed by
 * a parenthesis into a function with one argument, highest precedence.
 * The UNIDOR macro is for unary functions that can be followed by the //
 * operator (such as C<shift // 0>).
 */
#define UNI3(f,x,have_x) { \
        pl_yylval.ival = f; \
        if (have_x) PL_expect = x; \
        PL_bufptr = s; \
        PL_last_uni = PL_oldbufptr; \
        PL_last_lop_op = f; \
        if (*s == '(') \
            return REPORT( (int)FUNC1 ); \
        s = PEEKSPACE(s); \
        return REPORT( *s=='(' ? (int)FUNC1 : (int)UNIOP ); \
        }
#define UNI(f)    UNI3(f,XTERM,1)
#define UNIDOR(f) UNI3(f,XTERMORDORDOR,1)
#define UNIPROTO(f,optional) { \
        if (optional) PL_last_uni = PL_oldbufptr; \
        OPERATOR(f); \
        }

#define UNIBRACK(f) UNI3(f,0,0)

/* grandfather return to old style */
#define OLDLOP(f) \
        do { \
            if (!PL_lex_allbrackets && PL_lex_fakeeof > LEX_FAKEEOF_LOWLOGIC) \
                PL_lex_fakeeof = LEX_FAKEEOF_LOWLOGIC; \
            pl_yylval.ival = (f); \
            PL_expect = XTERM; \
            PL_bufptr = s; \
            return (int)LSTOP; \
        } while(0)

#ifdef DEBUGGING

/* how to interpret the pl_yylval associated with the token */
enum token_type {
    TOKENTYPE_NONE,
    TOKENTYPE_IVAL,
    TOKENTYPE_OPNUM, /* pl_yylval.ival contains an opcode number */
    TOKENTYPE_PVAL,
    TOKENTYPE_OPVAL,
    TOKENTYPE_GVVAL
};

static struct debug_tokens {
    const int token;
    enum token_type type;
    const char *name;
} const debug_tokens[] =
{
    { ADDOP,            TOKENTYPE_OPNUM,        "ADDOP" },
    { ANDAND,           TOKENTYPE_NONE,         "ANDAND" },
    { ANDOP,            TOKENTYPE_NONE,         "ANDOP" },
    { ANONSUB,          TOKENTYPE_IVAL,         "ANONSUB" },
    { ARROW,            TOKENTYPE_NONE,         "ARROW" },
    { ASSIGNOP,         TOKENTYPE_OPNUM,        "ASSIGNOP" },
    { BITANDOP,         TOKENTYPE_OPNUM,        "BITANDOP" },
    { BITOROP,          TOKENTYPE_OPNUM,        "BITOROP" },
    { COLONATTR,        TOKENTYPE_NONE,         "COLONATTR" },
    { CONTINUE,         TOKENTYPE_NONE,         "CONTINUE" },
    { DEFAULT,          TOKENTYPE_NONE,         "DEFAULT" },
    { DO,               TOKENTYPE_NONE,         "DO" },
    { DOLSHARP,         TOKENTYPE_NONE,         "DOLSHARP" },
    { DORDOR,           TOKENTYPE_NONE,         "DORDOR" },
    { DOROP,            TOKENTYPE_OPNUM,        "DOROP" },
    { DOTDOT,           TOKENTYPE_IVAL,         "DOTDOT" },
    { ELSE,             TOKENTYPE_NONE,         "ELSE" },
    { ELSIF,            TOKENTYPE_IVAL,         "ELSIF" },
    { EQOP,             TOKENTYPE_OPNUM,        "EQOP" },
    { FOR,              TOKENTYPE_IVAL,         "FOR" },
    { FORMAT,           TOKENTYPE_NONE,         "FORMAT" },
    { FUNC,             TOKENTYPE_OPNUM,        "FUNC" },
    { FUNC0,            TOKENTYPE_OPNUM,        "FUNC0" },
    { FUNC0OP,          TOKENTYPE_OPVAL,        "FUNC0OP" },
    { FUNC0SUB,         TOKENTYPE_OPVAL,        "FUNC0SUB" },
    { FUNC1,            TOKENTYPE_OPNUM,        "FUNC1" },
    { FUNCMETH,         TOKENTYPE_OPVAL,        "FUNCMETH" },
    { GIVEN,            TOKENTYPE_IVAL,         "GIVEN" },
    { HASHBRACK,        TOKENTYPE_NONE,         "HASHBRACK" },
    { IF,               TOKENTYPE_IVAL,         "IF" },
    { LABEL,            TOKENTYPE_OPVAL,        "LABEL" },
    { LOCAL,            TOKENTYPE_IVAL,         "LOCAL" },
    { LOOPEX,           TOKENTYPE_OPNUM,        "LOOPEX" },
    { LSTOP,            TOKENTYPE_OPNUM,        "LSTOP" },
    { LSTOPSUB,         TOKENTYPE_OPVAL,        "LSTOPSUB" },
    { MATCHOP,          TOKENTYPE_OPNUM,        "MATCHOP" },
    { METHOD,           TOKENTYPE_OPVAL,        "METHOD" },
    { MULOP,            TOKENTYPE_OPNUM,        "MULOP" },
    { MY,               TOKENTYPE_IVAL,         "MY" },
    { MYSUB,            TOKENTYPE_NONE,         "MYSUB" },
    { NOAMP,            TOKENTYPE_NONE,         "NOAMP" },
    { NOTOP,            TOKENTYPE_NONE,         "NOTOP" },
    { OROP,             TOKENTYPE_IVAL,         "OROP" },
    { OROR,             TOKENTYPE_NONE,         "OROR" },
    { PACKAGE,          TOKENTYPE_NONE,         "PACKAGE" },
    { PLUGEXPR,         TOKENTYPE_OPVAL,        "PLUGEXPR" },
    { PLUGSTMT,         TOKENTYPE_OPVAL,        "PLUGSTMT" },
    { PMFUNC,           TOKENTYPE_OPVAL,        "PMFUNC" },
    { POSTDEC,          TOKENTYPE_NONE,         "POSTDEC" },
    { POSTINC,          TOKENTYPE_NONE,         "POSTINC" },
    { POWOP,            TOKENTYPE_OPNUM,        "POWOP" },
    { PREDEC,           TOKENTYPE_NONE,         "PREDEC" },
    { PREINC,           TOKENTYPE_NONE,         "PREINC" },
    { PRIVATEREF,       TOKENTYPE_OPVAL,        "PRIVATEREF" },
    { REFGEN,           TOKENTYPE_NONE,         "REFGEN" },
    { RELOP,            TOKENTYPE_OPNUM,        "RELOP" },
    { SHIFTOP,          TOKENTYPE_OPNUM,        "SHIFTOP" },
    { SUB,              TOKENTYPE_NONE,         "SUB" },
    { THING,            TOKENTYPE_OPVAL,        "THING" },
    { UMINUS,           TOKENTYPE_NONE,         "UMINUS" },
    { UNIOP,            TOKENTYPE_OPNUM,        "UNIOP" },
    { UNIOPSUB,         TOKENTYPE_OPVAL,        "UNIOPSUB" },
    { UNLESS,           TOKENTYPE_IVAL,         "UNLESS" },
    { UNTIL,            TOKENTYPE_IVAL,         "UNTIL" },
    { USE,              TOKENTYPE_IVAL,         "USE" },
    { WHEN,             TOKENTYPE_IVAL,         "WHEN" },
    { WHILE,            TOKENTYPE_IVAL,         "WHILE" },
    { WORD,             TOKENTYPE_OPVAL,        "WORD" },
    { YADAYADA,         TOKENTYPE_IVAL,         "YADAYADA" },
    { 0,                TOKENTYPE_NONE,         NULL }
};

/* dump the returned token in rv, plus any optional arg in pl_yylval */

STATIC int
S_tokereport(pTHX_ I32 rv, const YYSTYPE* lvalp)
{
    dVAR;

    PERL_ARGS_ASSERT_TOKEREPORT;

    if (DEBUG_T_TEST) {
        const char *name = NULL;
        enum token_type type = TOKENTYPE_NONE;
        const struct debug_tokens *p;
        SV* const report = newSVpvs("<== ");

        for (p = debug_tokens; p->token; p++) {
            if (p->token == (int)rv) {
                name = p->name;
                type = p->type;
                break;
            }
        }
        if (name)
            Perl_sv_catpv(aTHX_ report, name);
        else if ((char)rv > ' ' && (char)rv < '~')
            Perl_sv_catpvf(aTHX_ report, "'%c'", (char)rv);
        else if (!rv)
            sv_catpvs(report, "EOF");
        else
            Perl_sv_catpvf(aTHX_ report, "?? %"IVdf, (IV)rv);
        switch (type) {
        case TOKENTYPE_NONE:
        case TOKENTYPE_GVVAL: /* doesn't appear to be used */
            break;
        case TOKENTYPE_IVAL:
            Perl_sv_catpvf(aTHX_ report, "(ival=%"IVdf")", (IV)lvalp->ival);
            break;
        case TOKENTYPE_OPNUM:
            Perl_sv_catpvf(aTHX_ report, "(ival=op_%s)",
                                    PL_op_name[lvalp->ival]);
            break;
        case TOKENTYPE_PVAL:
            Perl_sv_catpvf(aTHX_ report, "(pval=\"%s\")", lvalp->pval);
            break;
        case TOKENTYPE_OPVAL:
            if (lvalp->opval) {
                Perl_sv_catpvf(aTHX_ report, "(opval=op_%s)",
                                    PL_op_name[lvalp->opval->op_type]);
                if (lvalp->opval->op_type == OP_CONST) {
                    Perl_sv_catpvf(aTHX_ report, " %s",
                        SvPEEK(cSVOPx_sv(lvalp->opval)));
                }

            }
            else
                sv_catpvs(report, "(opval=null)");
            break;
        }
        PerlIO_printf(Perl_debug_log, "### %s\n\n", SvPV_nolen_const(report));
    };
    return (int)rv;
}


/* print the buffer with suitable escapes */

STATIC void
S_printbuf(pTHX_ const char *const fmt, const char *const s)
{
    SV* const tmp = newSVpvs("");

    PERL_ARGS_ASSERT_PRINTBUF;

    PerlIO_printf(Perl_debug_log, fmt, pv_display(tmp, s, strlen(s), 0, 60));
    SvREFCNT_dec(tmp);
}

#endif

static int
S_deprecate_commaless_var_list(pTHX) {
    PL_expect = XTERM;
    deprecate("comma-less variable list");
    return REPORT(','); /* grandfather non-comma-format format */
}

/*
 * S_ao
 *
 * This subroutine detects &&=, ||=, and //= and turns an ANDAND, OROR or DORDOR
 * into an OP_ANDASSIGN, OP_ORASSIGN, or OP_DORASSIGN
 */

STATIC int
S_ao(pTHX_ int toketype)
{
    dVAR;
    if (*PL_bufptr == '=') {
        PL_bufptr++;
        if (toketype == ANDAND)
            pl_yylval.ival = OP_ANDASSIGN;
        else if (toketype == OROR)
            pl_yylval.ival = OP_ORASSIGN;
        else if (toketype == DORDOR)
            pl_yylval.ival = OP_DORASSIGN;
        toketype = ASSIGNOP;
    }
    return toketype;
}

/*
 * S_no_op
 * When Perl expects an operator and finds something else, no_op
 * prints the warning.  It always prints "<something> found where
 * operator expected.  It prints "Missing semicolon on previous line?"
 * if the surprise occurs at the start of the line.  "do you need to
 * predeclare ..." is printed out for code like "sub bar; foo bar $x"
 * where the compiler doesn't know if foo is a method call or a function.
 * It prints "Missing operator before end of line" if there's nothing
 * after the missing operator, or "... before <...>" if there is something
 * after the missing operator.
 */

STATIC void
S_no_op(pTHX_ const char *const what, char *s)
{
    dVAR;
    char * const oldbp = PL_bufptr;
    const bool is_first = (PL_oldbufptr == PL_linestart);

    PERL_ARGS_ASSERT_NO_OP;

    if (!s)
        s = oldbp;
    else
        PL_bufptr = s;
    yywarn(Perl_form(aTHX_ "%s found where operator expected", what), UTF ? SVf_UTF8 : 0);
    if (ckWARN_d(WARN_SYNTAX)) {
        if (is_first)
            Perl_warner(aTHX_ packWARN(WARN_SYNTAX),
                    "\t(Missing semicolon on previous line?)\n");
        else if (PL_oldoldbufptr && isIDFIRST_lazy_if(PL_oldoldbufptr,UTF)) {
            const char *t;
            for (t = PL_oldoldbufptr; (isALNUM_lazy_if(t,UTF) || *t == ':');
                                                            t += UTF ? UTF8SKIP(t) : 1)
                NOOP;
            if (t < PL_bufptr && isSPACE(*t))
                Perl_warner(aTHX_ packWARN(WARN_SYNTAX),
                        "\t(Do you need to predeclare %"SVf"?)\n",
                    SVfARG(newSVpvn_flags(PL_oldoldbufptr, (STRLEN)(t - PL_oldoldbufptr),
                                   SVs_TEMP | (UTF ? SVf_UTF8 : 0))));
        }
        else {
            assert(s >= oldbp);
            Perl_warner(aTHX_ packWARN(WARN_SYNTAX),
                    "\t(Missing operator before %"SVf"?)\n",
                    SVfARG(newSVpvn_flags(oldbp, (STRLEN)(s - oldbp),
                                    SVs_TEMP | (UTF ? SVf_UTF8 : 0))));
        }
    }
    PL_bufptr = oldbp;
}

/*
 * S_missingterm
 * Complain about missing quote/regexp/heredoc terminator.
 * If it's called with NULL then it cauterizes the line buffer.
 * If we're in a delimited string and the delimiter is a control
 * character, it's reformatted into a two-char sequence like ^C.
 * This is fatal.
 */

STATIC void
S_missingterm(pTHX_ char *s)
{
    dVAR;
    char tmpbuf[3];
    char q;
    if (s) {
        char * const nl = strrchr(s,'\n');
        if (nl)
            *nl = '\0';
    }
    else if (isCNTRL(PL_multi_close)) {
        *tmpbuf = '^';
        tmpbuf[1] = (char)toCTRL(PL_multi_close);
        tmpbuf[2] = '\0';
        s = tmpbuf;
    }
    else {
        *tmpbuf = (char)PL_multi_close;
        tmpbuf[1] = '\0';
        s = tmpbuf;
    }
    q = strchr(s,'"') ? '\'' : '"';
    Perl_croak(aTHX_ "Can't find string terminator %c%s%c anywhere before EOF",q,s,q);
}

#include "feature.h"

/*
 * Check whether the named feature is enabled.
 */
bool
Perl_feature_is_enabled(pTHX_ const char *const name, STRLEN namelen)
{
    dVAR;
    char he_name[8 + MAX_FEATURE_LEN] = "feature_";

    PERL_ARGS_ASSERT_FEATURE_IS_ENABLED;

    assert(CURRENT_FEATURE_BUNDLE == FEATURE_BUNDLE_CUSTOM);

    if (namelen > MAX_FEATURE_LEN)
        return FALSE;
    memcpy(&he_name[8], name, namelen);

    return cBOOL(cop_hints_fetch_pvn(PL_curcop, he_name, 8 + namelen, 0,
                                     REFCOUNTED_HE_EXISTS));
}

/*
 * experimental text filters for win32 carriage-returns, utf16-to-utf8 and
 * utf16-to-utf8-reversed.
 */

#ifdef PERL_CR_FILTER
static void
strip_return(SV *sv)
{
    register const char *s = SvPVX_const(sv);
    register const char * const e = s + SvCUR(sv);

    PERL_ARGS_ASSERT_STRIP_RETURN;

    /* outer loop optimized to do nothing if there are no CR-LFs */
    while (s < e) {
        if (*s++ == '\r' && *s == '\n') {
            /* hit a CR-LF, need to copy the rest */
            register char *d = s - 1;
            *d++ = *s++;
            while (s < e) {
                if (*s == '\r' && s[1] == '\n')
                    s++;
                *d++ = *s++;
            }
            SvCUR(sv) -= s - d;
            return;
        }
    }
}

STATIC I32
S_cr_textfilter(pTHX_ int idx, SV *sv, int maxlen)
{
    const I32 count = FILTER_READ(idx+1, sv, maxlen);
    if (count > 0 && !maxlen)
        strip_return(sv);
    return count;
}
#endif

/*
=for apidoc Amx|void|lex_start|SV *line|PerlIO *rsfp|U32 flags

Creates and initialises a new lexer/parser state object, supplying
a context in which to lex and parse from a new source of Perl code.
A pointer to the new state object is placed in L</PL_parser>.  An entry
is made on the save stack so that upon unwinding the new state object
will be destroyed and the former value of L</PL_parser> will be restored.
Nothing else need be done to clean up the parsing context.

The code to be parsed comes from I<line> and I<rsfp>.  I<line>, if
non-null, provides a string (in SV form) containing code to be parsed.
A copy of the string is made, so subsequent modification of I<line>
does not affect parsing.  I<rsfp>, if non-null, provides an input stream
from which code will be read to be parsed.  If both are non-null, the
code in I<line> comes first and must consist of complete lines of input,
and I<rsfp> supplies the remainder of the source.

The I<flags> parameter is reserved for future use.  Currently it is only
used by perl internally, so extensions should always pass zero.

=cut
*/

/* LEX_START_SAME_FILTER indicates that this is not a new file, so it
   can share filters with the current parser.
   LEX_START_DONT_CLOSE indicates that the file handle wasn't opened by the
   caller, hence isn't owned by the parser, so shouldn't be closed on parser
   destruction. This is used to handle the case of defaulting to reading the
   script from the standard input because no filename was given on the command
   line (without getting confused by situation where STDIN has been closed, so
   the script handle is opened on fd 0)  */

void
Perl_lex_start(pTHX_ SV *line, PerlIO *rsfp, U32 flags)
{
    dVAR;
    const char *s = NULL;
    yy_parser *parser, *oparser;
    if (flags && flags & ~LEX_START_FLAGS)
        Perl_croak(aTHX_ "Lexing code internal error (%s)", "lex_start");

    /* create and initialise a parser */

    Newxz(parser, 1, yy_parser);
    parser->old_parser = oparser = PL_parser;
    PL_parser = parser;

    parser->stack = NULL;
    parser->ps = NULL;
    parser->stack_size = 0;

    /* on scope exit, free this parser and restore any outer one */
    SAVEPARSER(parser);
    parser->saved_curcop = PL_curcop;

    /* initialise lexer state */

#ifdef PERL_MAD
    parser->curforce = -1;
#else
    parser->nexttoke = 0;
#endif
    parser->error_count = oparser ? oparser->error_count : 0;
    parser->copline = NOLINE;
    parser->lex_state = LEX_NORMAL;
    parser->expect = XSTATE;
    parser->rsfp = rsfp;
    parser->rsfp_filters =
      !(flags & LEX_START_SAME_FILTER) || !oparser
        ? NULL
        : MUTABLE_AV(SvREFCNT_inc(
            oparser->rsfp_filters
             ? oparser->rsfp_filters
             : (oparser->rsfp_filters = newAV())
          ));

    Newx(parser->lex_brackstack, 120, char);
    Newx(parser->lex_casestack, 12, char);
    *parser->lex_casestack = '\0';

    if (line) {
        STRLEN len;
        s = SvPV_const(line, len);
        parser->linestr = flags & LEX_START_COPIED
                            ? SvREFCNT_inc_simple_NN(line)
                            : newSVpvn_flags(s, len, SvUTF8(line));
        if (!len || s[len-1] != ';')
            sv_catpvs(parser->linestr, "\n;");
    } else {
        parser->linestr = newSVpvs("\n;");
    }
    parser->oldoldbufptr =
        parser->oldbufptr =
        parser->bufptr =
        parser->linestart = SvPVX(parser->linestr);
    parser->bufend = parser->bufptr + SvCUR(parser->linestr);
    parser->last_lop = parser->last_uni = NULL;
    parser->lex_flags = flags & (LEX_IGNORE_UTF8_HINTS|LEX_EVALBYTES
                                 |LEX_DONT_CLOSE_RSFP);

    parser->in_pod = parser->filtered = 0;
}


/* delete a parser object */

void
Perl_parser_free(pTHX_  const yy_parser *parser)
{
    PERL_ARGS_ASSERT_PARSER_FREE;

    PL_curcop = parser->saved_curcop;
    SvREFCNT_dec(parser->linestr);

    if (PL_parser->lex_flags & LEX_DONT_CLOSE_RSFP)
        PerlIO_clearerr(parser->rsfp);
    else if (parser->rsfp && (!parser->old_parser ||
                (parser->old_parser && parser->rsfp != parser->old_parser->rsfp)))
        PerlIO_close(parser->rsfp);
    SvREFCNT_dec(parser->rsfp_filters);

    Safefree(parser->lex_brackstack);
    Safefree(parser->lex_casestack);
    PL_parser = parser->old_parser;
    Safefree(parser);
}


/*
=for apidoc AmxU|SV *|PL_parser-E<gt>linestr

Buffer scalar containing the chunk currently under consideration of the
text currently being lexed.  This is always a plain string scalar (for
which C<SvPOK> is true).  It is not intended to be used as a scalar by
normal scalar means; instead refer to the buffer directly by the pointer
variables described below.

The lexer maintains various C<char*> pointers to things in the
C<PL_parser-E<gt>linestr> buffer.  If C<PL_parser-E<gt>linestr> is ever
reallocated, all of these pointers must be updated.  Don't attempt to
do this manually, but rather use L</lex_grow_linestr> if you need to
reallocate the buffer.

The content of the text chunk in the buffer is commonly exactly one
complete line of input, up to and including a newline terminator,
but there are situations where it is otherwise.  The octets of the
buffer may be intended to be interpreted as either UTF-8 or Latin-1.
The function L</lex_bufutf8> tells you which.  Do not use the C<SvUTF8>
flag on this scalar, which may disagree with it.

For direct examination of the buffer, the variable
L</PL_parser-E<gt>bufend> points to the end of the buffer.  The current
lexing position is pointed to by L</PL_parser-E<gt>bufptr>.  Direct use
of these pointers is usually preferable to examination of the scalar
through normal scalar means.

=for apidoc AmxU|char *|PL_parser-E<gt>bufend

Direct pointer to the end of the chunk of text currently being lexed, the
end of the lexer buffer.  This is equal to C<SvPVX(PL_parser-E<gt>linestr)
+ SvCUR(PL_parser-E<gt>linestr)>.  A NUL character (zero octet) is
always located at the end of the buffer, and does not count as part of
the buffer's contents.

=for apidoc AmxU|char *|PL_parser-E<gt>bufptr

Points to the current position of lexing inside the lexer buffer.
Characters around this point may be freely examined, within
the range delimited by C<SvPVX(L</PL_parser-E<gt>linestr>)> and
L</PL_parser-E<gt>bufend>.  The octets of the buffer may be intended to be
interpreted as either UTF-8 or Latin-1, as indicated by L</lex_bufutf8>.

Lexing code (whether in the Perl core or not) moves this pointer past
the characters that it consumes.  It is also expected to perform some
bookkeeping whenever a newline character is consumed.  This movement
can be more conveniently performed by the function L</lex_read_to>,
which handles newlines appropriately.

Interpretation of the buffer's octets can be abstracted out by
using the slightly higher-level functions L</lex_peek_unichar> and
L</lex_read_unichar>.

=for apidoc AmxU|char *|PL_parser-E<gt>linestart

Points to the start of the current line inside the lexer buffer.
This is useful for indicating at which column an error occurred, and
not much else.  This must be updated by any lexing code that consumes
a newline; the function L</lex_read_to> handles this detail.

=cut
*/

/*
=for apidoc Amx|bool|lex_bufutf8

Indicates whether the octets in the lexer buffer
(L</PL_parser-E<gt>linestr>) should be interpreted as the UTF-8 encoding
of Unicode characters.  If not, they should be interpreted as Latin-1
characters.  This is analogous to the C<SvUTF8> flag for scalars.

In UTF-8 mode, it is not guaranteed that the lexer buffer actually
contains valid UTF-8.  Lexing code must be robust in the face of invalid
encoding.

The actual C<SvUTF8> flag of the L</PL_parser-E<gt>linestr> scalar
is significant, but not the whole story regarding the input character
encoding.  Normally, when a file is being read, the scalar contains octets
and its C<SvUTF8> flag is off, but the octets should be interpreted as
UTF-8 if the C<use utf8> pragma is in effect.  During a string eval,
however, the scalar may have the C<SvUTF8> flag on, and in this case its
octets should be interpreted as UTF-8 unless the C<use bytes> pragma
is in effect.  This logic may change in the future; use this function
instead of implementing the logic yourself.

=cut
*/

bool
Perl_lex_bufutf8(pTHX)
{
    return UTF;
}

/*
=for apidoc Amx|char *|lex_grow_linestr|STRLEN len

Reallocates the lexer buffer (L</PL_parser-E<gt>linestr>) to accommodate
at least I<len> octets (including terminating NUL).  Returns a
pointer to the reallocated buffer.  This is necessary before making
any direct modification of the buffer that would increase its length.
L</lex_stuff_pvn> provides a more convenient way to insert text into
the buffer.

Do not use C<SvGROW> or C<sv_grow> directly on C<PL_parser-E<gt>linestr>;
this function updates all of the lexer's variables that point directly
into the buffer.

=cut
*/

char *
Perl_lex_grow_linestr(pTHX_ STRLEN len)
{
    SV *linestr;
    char *buf;
    STRLEN bufend_pos, bufptr_pos, oldbufptr_pos, oldoldbufptr_pos;
    STRLEN linestart_pos, last_uni_pos, last_lop_pos, re_eval_start_pos;
    linestr = PL_parser->linestr;
    buf = SvPVX(linestr);
    if (len <= SvLEN(linestr))
        return buf;
    bufend_pos = PL_parser->bufend - buf;
    bufptr_pos = PL_parser->bufptr - buf;
    oldbufptr_pos = PL_parser->oldbufptr - buf;
    oldoldbufptr_pos = PL_parser->oldoldbufptr - buf;
    linestart_pos = PL_parser->linestart - buf;
    last_uni_pos = PL_parser->last_uni ? PL_parser->last_uni - buf : 0;
    last_lop_pos = PL_parser->last_lop ? PL_parser->last_lop - buf : 0;
    re_eval_start_pos = PL_sublex_info.re_eval_start ?
                            PL_sublex_info.re_eval_start - buf : 0;

    buf = sv_grow(linestr, len);

    PL_parser->bufend = buf + bufend_pos;
    PL_parser->bufptr = buf + bufptr_pos;
    PL_parser->oldbufptr = buf + oldbufptr_pos;
    PL_parser->oldoldbufptr = buf + oldoldbufptr_pos;
    PL_parser->linestart = buf + linestart_pos;
    if (PL_parser->last_uni)
        PL_parser->last_uni = buf + last_uni_pos;
    if (PL_parser->last_lop)
        PL_parser->last_lop = buf + last_lop_pos;
    if (PL_sublex_info.re_eval_start)
        PL_sublex_info.re_eval_start  = buf + re_eval_start_pos;
    return buf;
}

/*
=for apidoc Amx|void|lex_stuff_pvn|const char *pv|STRLEN len|U32 flags

Insert characters into the lexer buffer (L</PL_parser-E<gt>linestr>),
immediately after the current lexing point (L</PL_parser-E<gt>bufptr>),
reallocating the buffer if necessary.  This means that lexing code that
runs later will see the characters as if they had appeared in the input.
It is not recommended to do this as part of normal parsing, and most
uses of this facility run the risk of the inserted characters being
interpreted in an unintended manner.

The string to be inserted is represented by I<len> octets starting
at I<pv>.  These octets are interpreted as either UTF-8 or Latin-1,
according to whether the C<LEX_STUFF_UTF8> flag is set in I<flags>.
The characters are recoded for the lexer buffer, according to how the
buffer is currently being interpreted (L</lex_bufutf8>).  If a string
to be inserted is available as a Perl scalar, the L</lex_stuff_sv>
function is more convenient.

=cut
*/

void
Perl_lex_stuff_pvn(pTHX_ const char *pv, STRLEN len, U32 flags)
{
    dVAR;
    char *bufptr;
    PERL_ARGS_ASSERT_LEX_STUFF_PVN;
    if (flags & ~(LEX_STUFF_UTF8))
        Perl_croak(aTHX_ "Lexing code internal error (%s)", "lex_stuff_pvn");
    if (UTF) {
        if (flags & LEX_STUFF_UTF8) {
            goto plain_copy;
        } else {
            STRLEN highhalf = 0;
            const char *p, *e = pv+len;
            for (p = pv; p != e; p++)
                highhalf += !!(((U8)*p) & 0x80);
            if (!highhalf)
                goto plain_copy;
            lex_grow_linestr(SvCUR(PL_parser->linestr)+1+len+highhalf);
            bufptr = PL_parser->bufptr;
            Move(bufptr, bufptr+len+highhalf, PL_parser->bufend+1-bufptr, char);
            SvCUR_set(PL_parser->linestr,
                SvCUR(PL_parser->linestr) + len+highhalf);
            PL_parser->bufend += len+highhalf;
            for (p = pv; p != e; p++) {
                U8 c = (U8)*p;
                if (c & 0x80) {
                    *bufptr++ = (char)(0xc0 | (c >> 6));
                    *bufptr++ = (char)(0x80 | (c & 0x3f));
                } else {
                    *bufptr++ = (char)c;
                }
            }
        }
    } else {
        if (flags & LEX_STUFF_UTF8) {
            STRLEN highhalf = 0;
            const char *p, *e = pv+len;
            for (p = pv; p != e; p++) {
                U8 c = (U8)*p;
                if (c >= 0xc4) {
                    Perl_croak(aTHX_ "Lexing code attempted to stuff "
                                "non-Latin-1 character into Latin-1 input");
                } else if (c >= 0xc2 && p+1 != e &&
                            (((U8)p[1]) & 0xc0) == 0x80) {
                    p++;
                    highhalf++;
                } else if (c >= 0x80) {
                    /* malformed UTF-8 */
                    ENTER;
                    SAVESPTR(PL_warnhook);
                    PL_warnhook = PERL_WARNHOOK_FATAL;
                    utf8n_to_uvuni((U8*)p, e-p, NULL, 0);
                    LEAVE;
                }
            }
            if (!highhalf)
                goto plain_copy;
            lex_grow_linestr(SvCUR(PL_parser->linestr)+1+len-highhalf);
            bufptr = PL_parser->bufptr;
            Move(bufptr, bufptr+len-highhalf, PL_parser->bufend+1-bufptr, char);
            SvCUR_set(PL_parser->linestr,
                SvCUR(PL_parser->linestr) + len-highhalf);
            PL_parser->bufend += len-highhalf;
            for (p = pv; p != e; p++) {
                U8 c = (U8)*p;
                if (c & 0x80) {
                    *bufptr++ = (char)(((c & 0x3) << 6) | (p[1] & 0x3f));
                    p++;
                } else {
                    *bufptr++ = (char)c;
                }
            }
        } else {
            plain_copy:
            lex_grow_linestr(SvCUR(PL_parser->linestr)+1+len);
            bufptr = PL_parser->bufptr;
            Move(bufptr, bufptr+len, PL_parser->bufend+1-bufptr, char);
            SvCUR_set(PL_parser->linestr, SvCUR(PL_parser->linestr) + len);
            PL_parser->bufend += len;
            Copy(pv, bufptr, len, char);
        }
    }
}

/*
=for apidoc Amx|void|lex_stuff_pv|const char *pv|U32 flags

Insert characters into the lexer buffer (L</PL_parser-E<gt>linestr>),
immediately after the current lexing point (L</PL_parser-E<gt>bufptr>),
reallocating the buffer if necessary.  This means that lexing code that
runs later will see the characters as if they had appeared in the input.
It is not recommended to do this as part of normal parsing, and most
uses of this facility run the risk of the inserted characters being
interpreted in an unintended manner.

The string to be inserted is represented by octets starting at I<pv>
and continuing to the first nul.  These octets are interpreted as either
UTF-8 or Latin-1, according to whether the C<LEX_STUFF_UTF8> flag is set
in I<flags>.  The characters are recoded for the lexer buffer, according
to how the buffer is currently being interpreted (L</lex_bufutf8>).
If it is not convenient to nul-terminate a string to be inserted, the
L</lex_stuff_pvn> function is more appropriate.

=cut
*/

void
Perl_lex_stuff_pv(pTHX_ const char *pv, U32 flags)
{
    PERL_ARGS_ASSERT_LEX_STUFF_PV;
    lex_stuff_pvn(pv, strlen(pv), flags);
}

/*
=for apidoc Amx|void|lex_stuff_sv|SV *sv|U32 flags

Insert characters into the lexer buffer (L</PL_parser-E<gt>linestr>),
immediately after the current lexing point (L</PL_parser-E<gt>bufptr>),
reallocating the buffer if necessary.  This means that lexing code that
runs later will see the characters as if they had appeared in the input.
It is not recommended to do this as part of normal parsing, and most
uses of this facility run the risk of the inserted characters being
interpreted in an unintended manner.

The string to be inserted is the string value of I<sv>.  The characters
are recoded for the lexer buffer, according to how the buffer is currently
being interpreted (L</lex_bufutf8>).  If a string to be inserted is
not already a Perl scalar, the L</lex_stuff_pvn> function avoids the
need to construct a scalar.

=cut
*/

void
Perl_lex_stuff_sv(pTHX_ SV *sv, U32 flags)
{
    char *pv;
    STRLEN len;
    PERL_ARGS_ASSERT_LEX_STUFF_SV;
    if (flags)
        Perl_croak(aTHX_ "Lexing code internal error (%s)", "lex_stuff_sv");
    pv = SvPV(sv, len);
    lex_stuff_pvn(pv, len, flags | (SvUTF8(sv) ? LEX_STUFF_UTF8 : 0));
}

/*
=for apidoc Amx|void|lex_unstuff|char *ptr

Discards text about to be lexed, from L</PL_parser-E<gt>bufptr> up to
I<ptr>.  Text following I<ptr> will be moved, and the buffer shortened.
This hides the discarded text from any lexing code that runs later,
as if the text had never appeared.

This is not the normal way to consume lexed text.  For that, use
L</lex_read_to>.

=cut
*/

void
Perl_lex_unstuff(pTHX_ char *ptr)
{
    char *buf, *bufend;
    STRLEN unstuff_len;
    PERL_ARGS_ASSERT_LEX_UNSTUFF;
    buf = PL_parser->bufptr;
    if (ptr < buf)
        Perl_croak(aTHX_ "Lexing code internal error (%s)", "lex_unstuff");
    if (ptr == buf)
        return;
    bufend = PL_parser->bufend;
    if (ptr > bufend)
        Perl_croak(aTHX_ "Lexing code internal error (%s)", "lex_unstuff");
    unstuff_len = ptr - buf;
    Move(ptr, buf, bufend+1-ptr, char);
    SvCUR_set(PL_parser->linestr, SvCUR(PL_parser->linestr) - unstuff_len);
    PL_parser->bufend = bufend - unstuff_len;
}

/*
=for apidoc Amx|void|lex_read_to|char *ptr

Consume text in the lexer buffer, from L</PL_parser-E<gt>bufptr> up
to I<ptr>.  This advances L</PL_parser-E<gt>bufptr> to match I<ptr>,
performing the correct bookkeeping whenever a newline character is passed.
This is the normal way to consume lexed text.

Interpretation of the buffer's octets can be abstracted out by
using the slightly higher-level functions L</lex_peek_unichar> and
L</lex_read_unichar>.

=cut
*/

void
Perl_lex_read_to(pTHX_ char *ptr)
{
    char *s;
    PERL_ARGS_ASSERT_LEX_READ_TO;
    s = PL_parser->bufptr;
    if (ptr < s || ptr > PL_parser->bufend)
        Perl_croak(aTHX_ "Lexing code internal error (%s)", "lex_read_to");
    for (; s != ptr; s++)
        if (*s == '\n') {
            CopLINE_inc(PL_curcop);
            PL_parser->linestart = s+1;
        }
    PL_parser->bufptr = ptr;
}

/*
=for apidoc Amx|void|lex_discard_to|char *ptr

Discards the first part of the L</PL_parser-E<gt>linestr> buffer,
up to I<ptr>.  The remaining content of the buffer will be moved, and
all pointers into the buffer updated appropriately.  I<ptr> must not
be later in the buffer than the position of L</PL_parser-E<gt>bufptr>:
it is not permitted to discard text that has yet to be lexed.

Normally it is not necessarily to do this directly, because it suffices to
use the implicit discarding behaviour of L</lex_next_chunk> and things
based on it.  However, if a token stretches across multiple lines,
and the lexing code has kept multiple lines of text in the buffer for
that purpose, then after completion of the token it would be wise to
explicitly discard the now-unneeded earlier lines, to avoid future
multi-line tokens growing the buffer without bound.

=cut
*/

void
Perl_lex_discard_to(pTHX_ char *ptr)
{
    char *buf;
    STRLEN discard_len;
    PERL_ARGS_ASSERT_LEX_DISCARD_TO;
    buf = SvPVX(PL_parser->linestr);
    if (ptr < buf)
        Perl_croak(aTHX_ "Lexing code internal error (%s)", "lex_discard_to");
    if (ptr == buf)
        return;
    if (ptr > PL_parser->bufptr)
        Perl_croak(aTHX_ "Lexing code internal error (%s)", "lex_discard_to");
    discard_len = ptr - buf;
    if (PL_parser->oldbufptr < ptr)
        PL_parser->oldbufptr = ptr;
    if (PL_parser->oldoldbufptr < ptr)
        PL_parser->oldoldbufptr = ptr;
    if (PL_parser->last_uni && PL_parser->last_uni < ptr)
        PL_parser->last_uni = NULL;
    if (PL_parser->last_lop && PL_parser->last_lop < ptr)
        PL_parser->last_lop = NULL;
    Move(ptr, buf, PL_parser->bufend+1-ptr, char);
    SvCUR_set(PL_parser->linestr, SvCUR(PL_parser->linestr) - discard_len);
    PL_parser->bufend -= discard_len;
    PL_parser->bufptr -= discard_len;
    PL_parser->oldbufptr -= discard_len;
    PL_parser->oldoldbufptr -= discard_len;
    if (PL_parser->last_uni)
        PL_parser->last_uni -= discard_len;
    if (PL_parser->last_lop)
        PL_parser->last_lop -= discard_len;
}

/*
=for apidoc Amx|bool|lex_next_chunk|U32 flags

Reads in the next chunk of text to be lexed, appending it to
L</PL_parser-E<gt>linestr>.  This should be called when lexing code has
looked to the end of the current chunk and wants to know more.  It is
usual, but not necessary, for lexing to have consumed the entirety of
the current chunk at this time.

If L</PL_parser-E<gt>bufptr> is pointing to the very end of the current
chunk (i.e., the current chunk has been entirely consumed), normally the
current chunk will be discarded at the same time that the new chunk is
read in.  If I<flags> includes C<LEX_KEEP_PREVIOUS>, the current chunk
will not be discarded.  If the current chunk has not been entirely
consumed, then it will not be discarded regardless of the flag.

Returns true if some new text was added to the buffer, or false if the
buffer has reached the end of the input text.

=cut
*/

#define LEX_FAKE_EOF 0x80000000

bool
Perl_lex_next_chunk(pTHX_ U32 flags)
{
    SV *linestr;
    char *buf;
    STRLEN old_bufend_pos, new_bufend_pos;
    STRLEN bufptr_pos, oldbufptr_pos, oldoldbufptr_pos;
    STRLEN linestart_pos, last_uni_pos, last_lop_pos;
    bool got_some_for_debugger = 0;
    bool got_some;
    if (flags & ~(LEX_KEEP_PREVIOUS|LEX_FAKE_EOF))
        Perl_croak(aTHX_ "Lexing code internal error (%s)", "lex_next_chunk");
    linestr = PL_parser->linestr;
    buf = SvPVX(linestr);
    if (!(flags & LEX_KEEP_PREVIOUS) &&
            PL_parser->bufptr == PL_parser->bufend) {
        old_bufend_pos = bufptr_pos = oldbufptr_pos = oldoldbufptr_pos = 0;
        linestart_pos = 0;
        if (PL_parser->last_uni != PL_parser->bufend)
            PL_parser->last_uni = NULL;
        if (PL_parser->last_lop != PL_parser->bufend)
            PL_parser->last_lop = NULL;
        last_uni_pos = last_lop_pos = 0;
        *buf = 0;
        SvCUR(linestr) = 0;
    } else {
        old_bufend_pos = PL_parser->bufend - buf;
        bufptr_pos = PL_parser->bufptr - buf;
        oldbufptr_pos = PL_parser->oldbufptr - buf;
        oldoldbufptr_pos = PL_parser->oldoldbufptr - buf;
        linestart_pos = PL_parser->linestart - buf;
        last_uni_pos = PL_parser->last_uni ? PL_parser->last_uni - buf : 0;
        last_lop_pos = PL_parser->last_lop ? PL_parser->last_lop - buf : 0;
    }
    if (flags & LEX_FAKE_EOF) {
        goto eof;
    } else if (!PL_parser->rsfp && !PL_parser->filtered) {
        got_some = 0;
    } else if (filter_gets(linestr, old_bufend_pos)) {
        got_some = 1;
        got_some_for_debugger = 1;
    } else {
        if (!SvPOK(linestr))   /* can get undefined by filter_gets */
            sv_setpvs(linestr, "");
        eof:
        /* End of real input.  Close filehandle (unless it was STDIN),
         * then add implicit termination.
         */
        if (PL_parser->lex_flags & LEX_DONT_CLOSE_RSFP)
            PerlIO_clearerr(PL_parser->rsfp);
        else if (PL_parser->rsfp)
            (void)PerlIO_close(PL_parser->rsfp);
        PL_parser->rsfp = NULL;
        PL_parser->in_pod = PL_parser->filtered = 0;
#ifdef PERL_MAD
        if (PL_madskills && !PL_in_eval && (PL_minus_p || PL_minus_n))
            PL_faketokens = 1;
#endif
        if (!PL_in_eval && PL_minus_p) {
            sv_catpvs(linestr,
                /*{*/";}continue{print or die qq(-p destination: $!\\n);}");
            PL_minus_n = PL_minus_p = 0;
        } else if (!PL_in_eval && PL_minus_n) {
            sv_catpvs(linestr, /*{*/";}");
            PL_minus_n = 0;
        } else
            sv_catpvs(linestr, ";");
        got_some = 1;
    }
    buf = SvPVX(linestr);
    new_bufend_pos = SvCUR(linestr);
    PL_parser->bufend = buf + new_bufend_pos;
    PL_parser->bufptr = buf + bufptr_pos;
    PL_parser->oldbufptr = buf + oldbufptr_pos;
    PL_parser->oldoldbufptr = buf + oldoldbufptr_pos;
    PL_parser->linestart = buf + linestart_pos;
    if (PL_parser->last_uni)
        PL_parser->last_uni = buf + last_uni_pos;
    if (PL_parser->last_lop)
        PL_parser->last_lop = buf + last_lop_pos;
    if (got_some_for_debugger && (PERLDB_LINE || PERLDB_SAVESRC) &&
            PL_curstash != PL_debstash) {
        /* debugger active and we're not compiling the debugger code,
         * so store the line into the debugger's array of lines
         */
        update_debugger_info(NULL, buf+old_bufend_pos,
            new_bufend_pos-old_bufend_pos);
    }
    return got_some;
}

/*
=for apidoc Amx|I32|lex_peek_unichar|U32 flags

Looks ahead one (Unicode) character in the text currently being lexed.
Returns the codepoint (unsigned integer value) of the next character,
or -1 if lexing has reached the end of the input text.  To consume the
peeked character, use L</lex_read_unichar>.

If the next character is in (or extends into) the next chunk of input
text, the next chunk will be read in.  Normally the current chunk will be
discarded at the same time, but if I<flags> includes C<LEX_KEEP_PREVIOUS>
then the current chunk will not be discarded.

If the input is being interpreted as UTF-8 and a UTF-8 encoding error
is encountered, an exception is generated.

=cut
*/

I32
Perl_lex_peek_unichar(pTHX_ U32 flags)
{
    dVAR;
    char *s, *bufend;
    if (flags & ~(LEX_KEEP_PREVIOUS))
        Perl_croak(aTHX_ "Lexing code internal error (%s)", "lex_peek_unichar");
    s = PL_parser->bufptr;
    bufend = PL_parser->bufend;
    if (UTF) {
        U8 head;
        I32 unichar;
        STRLEN len, retlen;
        if (s == bufend) {
            if (!lex_next_chunk(flags))
                return -1;
            s = PL_parser->bufptr;
            bufend = PL_parser->bufend;
        }
        head = (U8)*s;
        if (!(head & 0x80))
            return head;
        if (head & 0x40) {
            len = PL_utf8skip[head];
            while ((STRLEN)(bufend-s) < len) {
                if (!lex_next_chunk(flags | LEX_KEEP_PREVIOUS))
                    break;
                s = PL_parser->bufptr;
                bufend = PL_parser->bufend;
            }
        }
        unichar = utf8n_to_uvuni((U8*)s, bufend-s, &retlen, UTF8_CHECK_ONLY);
        if (retlen == (STRLEN)-1) {
            /* malformed UTF-8 */
            ENTER;
            SAVESPTR(PL_warnhook);
            PL_warnhook = PERL_WARNHOOK_FATAL;
            utf8n_to_uvuni((U8*)s, bufend-s, NULL, 0);
            LEAVE;
        }
        return unichar;
    } else {
        if (s == bufend) {
            if (!lex_next_chunk(flags))
                return -1;
            s = PL_parser->bufptr;
        }
        return (U8)*s;
    }
}

/*
=for apidoc Amx|I32|lex_read_unichar|U32 flags

Reads the next (Unicode) character in the text currently being lexed.
Returns the codepoint (unsigned integer value) of the character read,
and moves L</PL_parser-E<gt>bufptr> past the character, or returns -1
if lexing has reached the end of the input text.  To non-destructively
examine the next character, use L</lex_peek_unichar> instead.

If the next character is in (or extends into) the next chunk of input
text, the next chunk will be read in.  Normally the current chunk will be
discarded at the same time, but if I<flags> includes C<LEX_KEEP_PREVIOUS>
then the current chunk will not be discarded.

If the input is being interpreted as UTF-8 and a UTF-8 encoding error
is encountered, an exception is generated.

=cut
*/

I32
Perl_lex_read_unichar(pTHX_ U32 flags)
{
    I32 c;
    if (flags & ~(LEX_KEEP_PREVIOUS))
        Perl_croak(aTHX_ "Lexing code internal error (%s)", "lex_read_unichar");
    c = lex_peek_unichar(flags);
    if (c != -1) {
        if (c == '\n')
            CopLINE_inc(PL_curcop);
        if (UTF)
            PL_parser->bufptr += UTF8SKIP(PL_parser->bufptr);
        else
            ++(PL_parser->bufptr);
    }
    return c;
}

/*
=for apidoc Amx|void|lex_read_space|U32 flags

Reads optional spaces, in Perl style, in the text currently being
lexed.  The spaces may include ordinary whitespace characters and
Perl-style comments.  C<#line> directives are processed if encountered.
L</PL_parser-E<gt>bufptr> is moved past the spaces, so that it points
at a non-space character (or the end of the input text).

If spaces extend into the next chunk of input text, the next chunk will
be read in.  Normally the current chunk will be discarded at the same
time, but if I<flags> includes C<LEX_KEEP_PREVIOUS> then the current
chunk will not be discarded.

=cut
*/

#define LEX_NO_NEXT_CHUNK 0x80000000

void
Perl_lex_read_space(pTHX_ U32 flags)
{
    char *s, *bufend;
    bool need_incline = 0;
    if (flags & ~(LEX_KEEP_PREVIOUS|LEX_NO_NEXT_CHUNK))
        Perl_croak(aTHX_ "Lexing code internal error (%s)", "lex_read_space");
#ifdef PERL_MAD
    if (PL_skipwhite) {
        sv_free(PL_skipwhite);
        PL_skipwhite = NULL;
    }
    if (PL_madskills)
        PL_skipwhite = newSVpvs("");
#endif /* PERL_MAD */
    s = PL_parser->bufptr;
    bufend = PL_parser->bufend;
    while (1) {
        char c = *s;
        if (c == '#') {
            do {
                c = *++s;
            } while (!(c == '\n' || (c == 0 && s == bufend)));
        } else if (c == '\n') {
            s++;
            PL_parser->linestart = s;
            if (s == bufend)
                need_incline = 1;
            else
                incline(s);
        } else if (isSPACE(c)) {
            s++;
        } else if (c == 0 && s == bufend) {
            bool got_more;
#ifdef PERL_MAD
            if (PL_madskills)
                sv_catpvn(PL_skipwhite, PL_parser->bufptr, s-PL_parser->bufptr);
#endif /* PERL_MAD */
            if (flags & LEX_NO_NEXT_CHUNK)
                break;
            PL_parser->bufptr = s;
            CopLINE_inc(PL_curcop);
            got_more = lex_next_chunk(flags);
            CopLINE_dec(PL_curcop);
            s = PL_parser->bufptr;
            bufend = PL_parser->bufend;
            if (!got_more)
                break;
            if (need_incline && PL_parser->rsfp) {
                incline(s);
                need_incline = 0;
            }
        } else {
            break;
        }
    }
#ifdef PERL_MAD
    if (PL_madskills)
        sv_catpvn(PL_skipwhite, PL_parser->bufptr, s-PL_parser->bufptr);
#endif /* PERL_MAD */
    PL_parser->bufptr = s;
}

/*
 * S_incline
 * This subroutine has nothing to do with tilting, whether at windmills
 * or pinball tables.  Its name is short for "increment line".  It
 * increments the current line number in CopLINE(PL_curcop) and checks
 * to see whether the line starts with a comment of the form
 *    # line 500 "foo.pm"
 * If so, it sets the current line number and file to the values in the comment.
 */

STATIC void
S_incline(pTHX_ const char *s)
{
    dVAR;
    const char *t;
    const char *n;
    const char *e;
    line_t line_num;

    PERL_ARGS_ASSERT_INCLINE;

    CopLINE_inc(PL_curcop);
    if (*s++ != '#')
        return;
    while (SPACE_OR_TAB(*s))
        s++;
    if (strnEQ(s, "line", 4))
        s += 4;
    else
        return;
    if (SPACE_OR_TAB(*s))
        s++;
    else
        return;
    while (SPACE_OR_TAB(*s))
        s++;
    if (!isDIGIT(*s))
        return;

    n = s;
    while (isDIGIT(*s))
        s++;
    if (!SPACE_OR_TAB(*s) && *s != '\r' && *s != '\n' && *s != '\0')
        return;
    while (SPACE_OR_TAB(*s))
        s++;
    if (*s == '"' && (t = strchr(s+1, '"'))) {
        s++;
        e = t + 1;
    }
    else {
        t = s;
        while (!isSPACE(*t))
            t++;
        e = t;
    }
    while (SPACE_OR_TAB(*e) || *e == '\r' || *e == '\f')
        e++;
    if (*e != '\n' && *e != '\0')
        return;         /* false alarm */

    line_num = atoi(n)-1;

    if (t - s > 0) {
        const STRLEN len = t - s;
        SV *const temp_sv = CopFILESV(PL_curcop);
        const char *cf;
        STRLEN tmplen;

        if (temp_sv) {
            cf = SvPVX(temp_sv);
            tmplen = SvCUR(temp_sv);
        } else {
            cf = NULL;
            tmplen = 0;
        }

        if (!PL_rsfp && !PL_parser->filtered) {
            /* must copy *{"::_<(eval N)[oldfilename:L]"}
             * to *{"::_<newfilename"} */
            /* However, the long form of evals is only turned on by the
               debugger - usually they're "(eval %lu)" */
            char smallbuf[128];
            char *tmpbuf;
            GV **gvp;
            STRLEN tmplen2 = len;
            if (tmplen + 2 <= sizeof smallbuf)
                tmpbuf = smallbuf;
            else
                Newx(tmpbuf, tmplen + 2, char);
            tmpbuf[0] = '_';
            tmpbuf[1] = '<';
            memcpy(tmpbuf + 2, cf, tmplen);
            tmplen += 2;
            gvp = (GV**)hv_fetch(PL_defstash, tmpbuf, tmplen, FALSE);
            if (gvp) {
                char *tmpbuf2;
                GV *gv2;

                if (tmplen2 + 2 <= sizeof smallbuf)
                    tmpbuf2 = smallbuf;
                else
                    Newx(tmpbuf2, tmplen2 + 2, char);

                if (tmpbuf2 != smallbuf || tmpbuf != smallbuf) {
                    /* Either they malloc'd it, or we malloc'd it,
                       so no prefix is present in ours.  */
                    tmpbuf2[0] = '_';
                    tmpbuf2[1] = '<';
                }

                memcpy(tmpbuf2 + 2, s, tmplen2);
                tmplen2 += 2;

                gv2 = *(GV**)hv_fetch(PL_defstash, tmpbuf2, tmplen2, TRUE);
                if (!isGV(gv2)) {
                    gv_init(gv2, PL_defstash, tmpbuf2, tmplen2, FALSE);
                    /* adjust ${"::_<newfilename"} to store the new file name */
                    GvSV(gv2) = newSVpvn(tmpbuf2 + 2, tmplen2 - 2);
                    /* The line number may differ. If that is the case,
                       alias the saved lines that are in the array.
                       Otherwise alias the whole array. */
                    if (CopLINE(PL_curcop) == line_num) {
                        GvHV(gv2) = MUTABLE_HV(SvREFCNT_inc(GvHV(*gvp)));
                        GvAV(gv2) = MUTABLE_AV(SvREFCNT_inc(GvAV(*gvp)));
                    }
                    else if (GvAV(*gvp)) {
                        AV * const av = GvAV(*gvp);
                        const I32 start = CopLINE(PL_curcop)+1;
                        I32 items = AvFILLp(av) - start;
                        if (items > 0) {
                            AV * const av2 = GvAVn(gv2);
                            SV **svp = AvARRAY(av) + start;
                            I32 l = (I32)line_num+1;
                            while (items--)
                                av_store(av2, l++, SvREFCNT_inc(*svp++));
                        }
                    }
                }

                if (tmpbuf2 != smallbuf) Safefree(tmpbuf2);
            }
            if (tmpbuf != smallbuf) Safefree(tmpbuf);
        }
        CopFILE_free(PL_curcop);
        CopFILE_setn(PL_curcop, s, len);
    }
    CopLINE_set(PL_curcop, line_num);
}

#ifdef PERL_MAD
/* skip space before PL_thistoken */

STATIC char *
S_skipspace0(pTHX_ register char *s)
{
    PERL_ARGS_ASSERT_SKIPSPACE0;

    s = skipspace(s);
    if (!PL_madskills)
        return s;
    if (PL_skipwhite) {
        if (!PL_thiswhite)
            PL_thiswhite = newSVpvs("");
        sv_catsv(PL_thiswhite, PL_skipwhite);
        sv_free(PL_skipwhite);
        PL_skipwhite = 0;
    }
    PL_realtokenstart = s - SvPVX(PL_linestr);
    return s;
}

/* skip space after PL_thistoken */

STATIC char *
S_skipspace1(pTHX_ register char *s)
{
    const char *start = s;
    I32 startoff = start - SvPVX(PL_linestr);

    PERL_ARGS_ASSERT_SKIPSPACE1;

    s = skipspace(s);
    if (!PL_madskills)
        return s;
    start = SvPVX(PL_linestr) + startoff;
    if (!PL_thistoken && PL_realtokenstart >= 0) {
        const char * const tstart = SvPVX(PL_linestr) + PL_realtokenstart;
        PL_thistoken = newSVpvn(tstart, start - tstart);
    }
    PL_realtokenstart = -1;
    if (PL_skipwhite) {
        if (!PL_nextwhite)
            PL_nextwhite = newSVpvs("");
        sv_catsv(PL_nextwhite, PL_skipwhite);
        sv_free(PL_skipwhite);
        PL_skipwhite = 0;
    }
    return s;
}

STATIC char *
S_skipspace2(pTHX_ register char *s, SV **svp)
{
    char *start;
    const I32 bufptroff = PL_bufptr - SvPVX(PL_linestr);
    const I32 startoff = s - SvPVX(PL_linestr);

    PERL_ARGS_ASSERT_SKIPSPACE2;

    s = skipspace(s);
    PL_bufptr = SvPVX(PL_linestr) + bufptroff;
    if (!PL_madskills || !svp)
        return s;
    start = SvPVX(PL_linestr) + startoff;
    if (!PL_thistoken && PL_realtokenstart >= 0) {
        char * const tstart = SvPVX(PL_linestr) + PL_realtokenstart;
        PL_thistoken = newSVpvn(tstart, start - tstart);
        PL_realtokenstart = -1;
    }
    if (PL_skipwhite) {
        if (!*svp)
            *svp = newSVpvs("");
        sv_setsv(*svp, PL_skipwhite);
        sv_free(PL_skipwhite);
        PL_skipwhite = 0;
    }
    
    return s;
}
#endif

STATIC void
S_update_debugger_info(pTHX_ SV *orig_sv, const char *const buf, STRLEN len)
{
    AV *av = CopFILEAVx(PL_curcop);
    if (av) {
        SV * const sv = newSV_type(SVt_PVMG);
        if (orig_sv)
            sv_setsv(sv, orig_sv);
        else
            sv_setpvn(sv, buf, len);
        (void)SvIOK_on(sv);
        SvIV_set(sv, 0);
        av_store(av, (I32)CopLINE(PL_curcop), sv);
    }
}

/*
 * S_skipspace
 * Called to gobble the appropriate amount and type of whitespace.
 * Skips comments as well.
 */

STATIC char *
S_skipspace(pTHX_ register char *s)
{
#ifdef PERL_MAD
    char *start = s;
#endif /* PERL_MAD */
    PERL_ARGS_ASSERT_SKIPSPACE;
#ifdef PERL_MAD
    if (PL_skipwhite) {
        sv_free(PL_skipwhite);
        PL_skipwhite = NULL;
    }
#endif /* PERL_MAD */
    if (PL_lex_formbrack && PL_lex_brackets <= PL_lex_formbrack) {
        while (s < PL_bufend && SPACE_OR_TAB(*s))
            s++;
    } else {
        STRLEN bufptr_pos = PL_bufptr - SvPVX(PL_linestr);
        PL_bufptr = s;
        lex_read_space(LEX_KEEP_PREVIOUS |
                (PL_sublex_info.sub_inwhat || PL_lex_state == LEX_FORMLINE ?
                    LEX_NO_NEXT_CHUNK : 0));
        s = PL_bufptr;
        PL_bufptr = SvPVX(PL_linestr) + bufptr_pos;
        if (PL_linestart > PL_bufptr)
            PL_bufptr = PL_linestart;
        return s;
    }
#ifdef PERL_MAD
    if (PL_madskills)
        PL_skipwhite = newSVpvn(start, s-start);
#endif /* PERL_MAD */
    return s;
}

/*
 * S_check_uni
 * Check the unary operators to ensure there's no ambiguity in how they're
 * used.  An ambiguous piece of code would be:
 *     rand + 5
 * This doesn't mean rand() + 5.  Because rand() is a unary operator,
 * the +5 is its argument.
 */

STATIC void
S_check_uni(pTHX)
{
    dVAR;
    const char *s;
    const char *t;

    if (PL_oldoldbufptr != PL_last_uni)
        return;
    while (isSPACE(*PL_last_uni))
        PL_last_uni++;
    s = PL_last_uni;
    while (isALNUM_lazy_if(s,UTF) || *s == '-')
        s++;
    if ((t = strchr(s, '(')) && t < PL_bufptr)
        return;

    Perl_ck_warner_d(aTHX_ packWARN(WARN_AMBIGUOUS),
                     "Warning: Use of \"%.*s\" without parentheses is ambiguous",
                     (int)(s - PL_last_uni), PL_last_uni);
}

/*
 * LOP : macro to build a list operator.  Its behaviour has been replaced
 * with a subroutine, S_lop() for which LOP is just another name.
 */

#define LOP(f,x) return lop(f,x,s)

/*
 * S_lop
 * Build a list operator (or something that might be one).  The rules:
 *  - if we have a next token, then it's a list operator [why?]
 *  - if the next thing is an opening paren, then it's a function
 *  - else it's a list operator
 */

STATIC I32
S_lop(pTHX_ I32 f, int x, char *s)
{
    dVAR;

    PERL_ARGS_ASSERT_LOP;

    pl_yylval.ival = f;
    CLINE;
    PL_expect = x;
    PL_bufptr = s;
    PL_last_lop = PL_oldbufptr;
    PL_last_lop_op = (OPCODE)f;
#ifdef PERL_MAD
    if (PL_lasttoke)
        goto lstop;
#else
    if (PL_nexttoke)
        goto lstop;
#endif
    if (*s == '(')
        return REPORT(FUNC);
    s = PEEKSPACE(s);
    if (*s == '(')
        return REPORT(FUNC);
    else {
        lstop:
        if (!PL_lex_allbrackets && PL_lex_fakeeof > LEX_FAKEEOF_LOWLOGIC)
            PL_lex_fakeeof = LEX_FAKEEOF_LOWLOGIC;
        return REPORT(LSTOP);
    }
}

#ifdef PERL_MAD
 /*
 * S_start_force
 * Sets up for an eventual force_next().  start_force(0) basically does
 * an unshift, while start_force(-1) does a push.  yylex removes items
 * on the "pop" end.
 */

STATIC void
S_start_force(pTHX_ int where)
{
    int i;

    if (where < 0)      /* so people can duplicate start_force(PL_curforce) */
        where = PL_lasttoke;
    assert(PL_curforce < 0 || PL_curforce == where);
    if (PL_curforce != where) {
        for (i = PL_lasttoke; i > where; --i) {
            PL_nexttoke[i] = PL_nexttoke[i-1];
        }
        PL_lasttoke++;
    }
    if (PL_curforce < 0)        /* in case of duplicate start_force() */
        Zero(&PL_nexttoke[where], 1, NEXTTOKE);
    PL_curforce = where;
    if (PL_nextwhite) {
        if (PL_madskills)
            curmad('^', newSVpvs(""));
        CURMAD('_', PL_nextwhite);
    }
}

STATIC void
S_curmad(pTHX_ char slot, SV *sv)
{
    MADPROP **where;

    if (!sv)
        return;
    if (PL_curforce < 0)
        where = &PL_thismad;
    else
        where = &PL_nexttoke[PL_curforce].next_mad;

    if (PL_faketokens)
        sv_setpvs(sv, "");
    else {
        if (!IN_BYTES) {
            if (UTF && is_utf8_string((U8*)SvPVX(sv), SvCUR(sv)))
                SvUTF8_on(sv);
            else if (PL_encoding) {
                sv_recode_to_utf8(sv, PL_encoding);
            }
        }
    }

    /* keep a slot open for the head of the list? */
    if (slot != '_' && *where && (*where)->mad_key == '^') {
        (*where)->mad_key = slot;
        sv_free(MUTABLE_SV(((*where)->mad_val)));
        (*where)->mad_val = (void*)sv;
    }
    else
        addmad(newMADsv(slot, sv), where, 0);
}
#else
#  define start_force(where)    NOOP
#  define curmad(slot, sv)      NOOP
#endif

/*
 * S_force_next
 * When the lexer realizes it knows the next token (for instance,
 * it is reordering tokens for the parser) then it can call S_force_next
 * to know what token to return the next time the lexer is called.  Caller
 * will need to set PL_nextval[] (or PL_nexttoke[].next_val with PERL_MAD),
 * and possibly PL_expect to ensure the lexer handles the token correctly.
 */

STATIC void
S_force_next(pTHX_ I32 type)
{
    dVAR;
#ifdef DEBUGGING
    if (DEBUG_T_TEST) {
        PerlIO_printf(Perl_debug_log, "### forced token:\n");
        tokereport(type, &NEXTVAL_NEXTTOKE);
    }
#endif
#ifdef PERL_MAD
    if (PL_curforce < 0)
        start_force(PL_lasttoke);
    PL_nexttoke[PL_curforce].next_type = type;
    if (PL_lex_state != LEX_KNOWNEXT)
        PL_lex_defer = PL_lex_state;
    PL_lex_state = LEX_KNOWNEXT;
    PL_lex_expect = PL_expect;
    PL_curforce = -1;
#else
    PL_nexttype[PL_nexttoke] = type;
    PL_nexttoke++;
    if (PL_lex_state != LEX_KNOWNEXT) {
        PL_lex_defer = PL_lex_state;
        PL_lex_expect = PL_expect;
        PL_lex_state = LEX_KNOWNEXT;
    }
#endif
}

void
Perl_yyunlex(pTHX)
{
    int yyc = PL_parser->yychar;
    if (yyc != YYEMPTY) {
        if (yyc) {
            start_force(-1);
            NEXTVAL_NEXTTOKE = PL_parser->yylval;
            if (yyc == '{'/*}*/ || yyc == HASHBRACK || yyc == '['/*]*/) {
                PL_lex_allbrackets--;
                PL_lex_brackets--;
                yyc |= (3<<24) | (PL_lex_brackstack[PL_lex_brackets] << 16);
            } else if (yyc == '('/*)*/) {
                PL_lex_allbrackets--;
                yyc |= (2<<24);
            }
            force_next(yyc);
        }
        PL_parser->yychar = YYEMPTY;
    }
}

STATIC SV *
S_newSV_maybe_utf8(pTHX_ const char *const start, STRLEN len)
{
    dVAR;
    SV * const sv = newSVpvn_utf8(start, len,
                                  !IN_BYTES
                                  && UTF
                                  && !is_ascii_string((const U8*)start, len)
                                  && is_utf8_string((const U8*)start, len));
    return sv;
}

/*
 * S_force_word
 * When the lexer knows the next thing is a word (for instance, it has
 * just seen -> and it knows that the next char is a word char, then
 * it calls S_force_word to stick the next word into the PL_nexttoke/val
 * lookahead.
 *
 * Arguments:
 *   char *start : buffer position (must be within PL_linestr)
 *   int token   : PL_next* will be this type of bare word (e.g., METHOD,WORD)
 *   int check_keyword : if true, Perl checks to make sure the word isn't
 *       a keyword (do this if the word is a label, e.g. goto FOO)
 *   int allow_pack : if true, : characters will also be allowed (require,
 *       use, etc. do this)
 *   int allow_initial_tick : used by the "sub" lexer only.
 */

STATIC char *
S_force_word(pTHX_ register char *start, int token, int check_keyword, int allow_pack, int allow_initial_tick)
{
    dVAR;
    register char *s;
    STRLEN len;

    PERL_ARGS_ASSERT_FORCE_WORD;

    start = SKIPSPACE1(start);
    s = start;
    if (isIDFIRST_lazy_if(s,UTF) ||
        (allow_pack && *s == ':') ||
        (allow_initial_tick && *s == '\'') )
    {
        s = scan_word(s, PL_tokenbuf, sizeof PL_tokenbuf, allow_pack, &len);
        if (check_keyword && keyword(PL_tokenbuf, len, 0))
            return start;
        start_force(PL_curforce);
        if (PL_madskills)
            curmad('X', newSVpvn(start,s-start));
        if (token == METHOD) {
            s = SKIPSPACE1(s);
            if (*s == '(')
                PL_expect = XTERM;
            else {
                PL_expect = XOPERATOR;
            }
        }
        if (PL_madskills)
            curmad('g', newSVpvs( "forced" ));
        NEXTVAL_NEXTTOKE.opval
            = (OP*)newSVOP(OP_CONST,0,
                           S_newSV_maybe_utf8(aTHX_ PL_tokenbuf, len));
        NEXTVAL_NEXTTOKE.opval->op_private |= OPpCONST_BARE;
        force_next(token);
    }
    return s;
}

/*
 * S_force_ident
 * Called when the lexer wants $foo *foo &foo etc, but the program
 * text only contains the "foo" portion.  The first argument is a pointer
 * to the "foo", and the second argument is the type symbol to prefix.
 * Forces the next token to be a "WORD".
 * Creates the symbol if it didn't already exist (via gv_fetchpv()).
 */

STATIC void
S_force_ident(pTHX_ register const char *s, int kind)
{
    dVAR;

    PERL_ARGS_ASSERT_FORCE_IDENT;

    if (*s) {
        const STRLEN len = strlen(s);
        OP* const o = (OP*)newSVOP(OP_CONST, 0, newSVpvn_flags(s, len,
                                                                UTF ? SVf_UTF8 : 0));
        start_force(PL_curforce);
        NEXTVAL_NEXTTOKE.opval = o;
        force_next(WORD);
        if (kind) {
            o->op_private = OPpCONST_ENTERED;
            /* XXX see note in pp_entereval() for why we forgo typo
               warnings if the symbol must be introduced in an eval.
               GSAR 96-10-12 */
            gv_fetchpvn_flags(s, len,
                              (PL_in_eval ? (GV_ADDMULTI | GV_ADDINEVAL)
                              : GV_ADD) | ( UTF ? SVf_UTF8 : 0 ),
                              kind == '$' ? SVt_PV :
                              kind == '@' ? SVt_PVAV :
                              kind == '%' ? SVt_PVHV :
                              SVt_PVGV
                              );
        }
    }
}

NV
Perl_str_to_version(pTHX_ SV *sv)
{
    NV retval = 0.0;
    NV nshift = 1.0;
    STRLEN len;
    const char *start = SvPV_const(sv,len);
    const char * const end = start + len;
    const bool utf = SvUTF8(sv) ? TRUE : FALSE;

    PERL_ARGS_ASSERT_STR_TO_VERSION;

    while (start < end) {
        STRLEN skip;
        UV n;
        if (utf)
            n = utf8n_to_uvchr((U8*)start, len, &skip, 0);
        else {
            n = *(U8*)start;
            skip = 1;
        }
        retval += ((NV)n)/nshift;
        start += skip;
        nshift *= 1000;
    }
    return retval;
}

/*
 * S_force_version
 * Forces the next token to be a version number.
 * If the next token appears to be an invalid version number, (e.g. "v2b"),
 * and if "guessing" is TRUE, then no new token is created (and the caller
 * must use an alternative parsing method).
 */

STATIC char *
S_force_version(pTHX_ char *s, int guessing)
{
    dVAR;
    OP *version = NULL;
    char *d;
#ifdef PERL_MAD
    I32 startoff = s - SvPVX(PL_linestr);
#endif

    PERL_ARGS_ASSERT_FORCE_VERSION;

    s = SKIPSPACE1(s);

    d = s;
    if (*d == 'v')
        d++;
    if (isDIGIT(*d)) {
        while (isDIGIT(*d) || *d == '_' || *d == '.')
            d++;
#ifdef PERL_MAD
        if (PL_madskills) {
            start_force(PL_curforce);
            curmad('X', newSVpvn(s,d-s));
        }
#endif
        if (*d == ';' || isSPACE(*d) || *d == '{' || *d == '}' || !*d) {
            SV *ver;
#ifdef USE_LOCALE_NUMERIC
            char *loc = savepv(setlocale(LC_NUMERIC, NULL));
            setlocale(LC_NUMERIC, "C");
#endif
            s = scan_num(s, &pl_yylval);
#ifdef USE_LOCALE_NUMERIC
            setlocale(LC_NUMERIC, loc);
            Safefree(loc);
#endif
            version = pl_yylval.opval;
            ver = cSVOPx(version)->op_sv;
            if (SvPOK(ver) && !SvNIOK(ver)) {
                SvUPGRADE(ver, SVt_PVNV);
                SvNV_set(ver, str_to_version(ver));
                SvNOK_on(ver);          /* hint that it is a version */
            }
        }
        else if (guessing) {
#ifdef PERL_MAD
            if (PL_madskills) {
                sv_free(PL_nextwhite);  /* let next token collect whitespace */
                PL_nextwhite = 0;
                s = SvPVX(PL_linestr) + startoff;
            }
#endif
            return s;
        }
    }

#ifdef PERL_MAD
    if (PL_madskills && !version) {
        sv_free(PL_nextwhite);  /* let next token collect whitespace */
        PL_nextwhite = 0;
        s = SvPVX(PL_linestr) + startoff;
    }
#endif
    /* NOTE: The parser sees the package name and the VERSION swapped */
    start_force(PL_curforce);
    NEXTVAL_NEXTTOKE.opval = version;
    force_next(WORD);

    return s;
}

/*
 * S_force_strict_version
 * Forces the next token to be a version number using strict syntax rules.
 */

STATIC char *
S_force_strict_version(pTHX_ char *s)
{
    dVAR;
    OP *version = NULL;
#ifdef PERL_MAD
    I32 startoff = s - SvPVX(PL_linestr);
#endif
    const char *errstr = NULL;

    PERL_ARGS_ASSERT_FORCE_STRICT_VERSION;

    while (isSPACE(*s)) /* leading whitespace */
        s++;

    if (is_STRICT_VERSION(s,&errstr)) {
        SV *ver = newSV(0);
        s = (char *)scan_version(s, ver, 0);
        version = newSVOP(OP_CONST, 0, ver);
    }
    else if ( (*s != ';' && *s != '{' && *s != '}' ) &&
            (s = SKIPSPACE1(s), (*s != ';' && *s != '{' && *s != '}' )))
    {
        PL_bufptr = s;
        if (errstr)
            yyerror(errstr); /* version required */
        return s;
    }

#ifdef PERL_MAD
    if (PL_madskills && !version) {
        sv_free(PL_nextwhite);  /* let next token collect whitespace */
        PL_nextwhite = 0;
        s = SvPVX(PL_linestr) + startoff;
    }
#endif
    /* NOTE: The parser sees the package name and the VERSION swapped */
    start_force(PL_curforce);
    NEXTVAL_NEXTTOKE.opval = version;
    force_next(WORD);

    return s;
}

/*
 * S_tokeq
 * Tokenize a quoted string passed in as an SV.  It finds the next
 * chunk, up to end of string or a backslash.  It may make a new
 * SV containing that chunk (if HINT_NEW_STRING is on).  It also
 * turns \\ into \.
 */

STATIC SV *
S_tokeq(pTHX_ SV *sv)
{
    dVAR;
    register char *s;
    register char *send;
    register char *d;
    STRLEN len = 0;
    SV *pv = sv;

    PERL_ARGS_ASSERT_TOKEQ;

    if (!SvLEN(sv))
        goto finish;

    s = SvPV_force(sv, len);
    if (SvTYPE(sv) >= SVt_PVIV && SvIVX(sv) == -1)
        goto finish;
    send = s + len;
    /* This is relying on the SV being "well formed" with a trailing '\0'  */
    while (s < send && !(*s == '\\' && s[1] == '\\'))
        s++;
    if (s == send)
        goto finish;
    d = s;
    if ( PL_hints & HINT_NEW_STRING ) {
        pv = newSVpvn_flags(SvPVX_const(pv), len, SVs_TEMP | SvUTF8(sv));
    }
    while (s < send) {
        if (*s == '\\') {
            if (s + 1 < send && (s[1] == '\\'))
                s++;            /* all that, just for this */
        }
        *d++ = *s++;
    }
    *d = '\0';
    SvCUR_set(sv, d - SvPVX_const(sv));
  finish:
    if ( PL_hints & HINT_NEW_STRING )
       return new_constant(NULL, 0, "q", sv, pv, "q", 1);
    return sv;
}

/*
 * Now come three functions related to double-quote context,
 * S_sublex_start, S_sublex_push, and S_sublex_done.  They're used when
 * converting things like "\u\Lgnat" into ucfirst(lc("gnat")).  They
 * interact with PL_lex_state, and create fake ( ... ) argument lists
 * to handle functions and concatenation.
 * For example,
 *   "foo\lbar"
 * is tokenised as
 *    stringify ( const[foo] concat lcfirst ( const[bar] ) )
 */

/*
 * S_sublex_start
 * Assumes that pl_yylval.ival is the op we're creating (e.g. OP_LCFIRST).
 *
 * Pattern matching will set PL_lex_op to the pattern-matching op to
 * make (we return THING if pl_yylval.ival is OP_NULL, PMFUNC otherwise).
 *
 * OP_CONST and OP_READLINE are easy--just make the new op and return.
 *
 * Everything else becomes a FUNC.
 *
 * Sets PL_lex_state to LEX_INTERPPUSH unless (ival was OP_NULL or we
 * had an OP_CONST or OP_READLINE).  This just sets us up for a
 * call to S_sublex_push().
 */

STATIC I32
S_sublex_start(pTHX)
{
    dVAR;
    register const I32 op_type = pl_yylval.ival;

    if (op_type == OP_NULL) {
        pl_yylval.opval = PL_lex_op;
        PL_lex_op = NULL;
        return THING;
    }
    if (op_type == OP_CONST || op_type == OP_READLINE) {
        SV *sv = tokeq(PL_lex_stuff);

        if (SvTYPE(sv) == SVt_PVIV) {
            /* Overloaded constants, nothing fancy: Convert to SVt_PV: */
            STRLEN len;
            const char * const p = SvPV_const(sv, len);
            SV * const nsv = newSVpvn_flags(p, len, SvUTF8(sv));
            SvREFCNT_dec(sv);
            sv = nsv;
        }
        pl_yylval.opval = (OP*)newSVOP(op_type, 0, sv);
        PL_lex_stuff = NULL;
        /* Allow <FH> // "foo" */
        if (op_type == OP_READLINE)
            PL_expect = XTERMORDORDOR;
        return THING;
    }
    else if (op_type == OP_BACKTICK && PL_lex_op) {
        /* readpipe() vas overriden */
        cSVOPx(cLISTOPx(cUNOPx(PL_lex_op)->op_first)->op_first->op_sibling)->op_sv = tokeq(PL_lex_stuff);
        pl_yylval.opval = PL_lex_op;
        PL_lex_op = NULL;
        PL_lex_stuff = NULL;
        return THING;
    }

    PL_sublex_info.super_state = PL_lex_state;
    PL_sublex_info.sub_inwhat = (U16)op_type;
    PL_sublex_info.sub_op = PL_lex_op;
    PL_lex_state = LEX_INTERPPUSH;

    PL_expect = XTERM;
    if (PL_lex_op) {
        pl_yylval.opval = PL_lex_op;
        PL_lex_op = NULL;
        return PMFUNC;
    }
    else
        return FUNC;
}

/*
 * S_sublex_push
 * Create a new scope to save the lexing state.  The scope will be
 * ended in S_sublex_done.  Returns a '(', starting the function arguments
 * to the uc, lc, etc. found before.
 * Sets PL_lex_state to LEX_INTERPCONCAT.
 */

STATIC I32
S_sublex_push(pTHX)
{
    dVAR;
    ENTER;

    PL_lex_state = PL_sublex_info.super_state;
    SAVEBOOL(PL_lex_dojoin);
    SAVEI32(PL_lex_brackets);
    SAVEI32(PL_lex_allbrackets);
    SAVEI8(PL_lex_fakeeof);
    SAVEI32(PL_lex_casemods);
    SAVEI32(PL_lex_starts);
    SAVEI8(PL_lex_state);
    SAVEPPTR(PL_sublex_info.re_eval_start);
    SAVEVPTR(PL_lex_inpat);
    SAVEI16(PL_lex_inwhat);
    SAVECOPLINE(PL_curcop);
    SAVEPPTR(PL_bufptr);
    SAVEPPTR(PL_bufend);
    SAVEPPTR(PL_oldbufptr);
    SAVEPPTR(PL_oldoldbufptr);
    SAVEPPTR(PL_last_lop);
    SAVEPPTR(PL_last_uni);
    SAVEPPTR(PL_linestart);
    SAVESPTR(PL_linestr);
    SAVEGENERICPV(PL_lex_brackstack);
    SAVEGENERICPV(PL_lex_casestack);

    PL_linestr = PL_lex_stuff;
    PL_lex_stuff = NULL;
    PL_sublex_info.re_eval_start = NULL;

    PL_bufend = PL_bufptr = PL_oldbufptr = PL_oldoldbufptr = PL_linestart
        = SvPVX(PL_linestr);
    PL_bufend += SvCUR(PL_linestr);
    PL_last_lop = PL_last_uni = NULL;
    SAVEFREESV(PL_linestr);

    PL_lex_dojoin = FALSE;
    PL_lex_brackets = 0;
    PL_lex_allbrackets = 0;
    PL_lex_fakeeof = LEX_FAKEEOF_NEVER;
    Newx(PL_lex_brackstack, 120, char);
    Newx(PL_lex_casestack, 12, char);
    PL_lex_casemods = 0;
    *PL_lex_casestack = '\0';
    PL_lex_starts = 0;
    PL_lex_state = LEX_INTERPCONCAT;
    CopLINE_set(PL_curcop, (line_t)PL_multi_start);

    PL_lex_inwhat = PL_sublex_info.sub_inwhat;
    if (PL_lex_inwhat == OP_TRANSR) PL_lex_inwhat = OP_TRANS;
    if (PL_lex_inwhat == OP_MATCH || PL_lex_inwhat == OP_QR || PL_lex_inwhat == OP_SUBST)
        PL_lex_inpat = PL_sublex_info.sub_op;
    else
        PL_lex_inpat = NULL;

    return '(';
}

/*
 * S_sublex_done
 * Restores lexer state after a S_sublex_push.
 */

STATIC I32
S_sublex_done(pTHX)
{
    dVAR;
    if (!PL_lex_starts++) {
        SV * const sv = newSVpvs("");
        if (SvUTF8(PL_linestr))
            SvUTF8_on(sv);
        PL_expect = XOPERATOR;
        pl_yylval.opval = (OP*)newSVOP(OP_CONST, 0, sv);
        return THING;
    }

    if (PL_lex_casemods) {              /* oops, we've got some unbalanced parens */
        PL_lex_state = LEX_INTERPCASEMOD;
        return yylex();
    }

    /* Is there a right-hand side to take care of? (s//RHS/ or tr//RHS/) */
    assert(PL_lex_inwhat != OP_TRANSR);
    if (PL_lex_repl && (PL_lex_inwhat == OP_SUBST || PL_lex_inwhat == OP_TRANS)) {
        PL_linestr = PL_lex_repl;
        PL_lex_inpat = 0;
        PL_bufend = PL_bufptr = PL_oldbufptr = PL_oldoldbufptr = PL_linestart = SvPVX(PL_linestr);
        PL_bufend += SvCUR(PL_linestr);
        PL_last_lop = PL_last_uni = NULL;
        SAVEFREESV(PL_linestr);
        PL_lex_dojoin = FALSE;
        PL_lex_brackets = 0;
        PL_lex_allbrackets = 0;
        PL_lex_fakeeof = LEX_FAKEEOF_NEVER;
        PL_lex_casemods = 0;
        *PL_lex_casestack = '\0';
        PL_lex_starts = 0;
        if (SvEVALED(PL_lex_repl)) {
            PL_lex_state = LEX_INTERPNORMAL;
            PL_lex_starts++;
            /*  we don't clear PL_lex_repl here, so that we can check later
                whether this is an evalled subst; that means we rely on the
                logic to ensure sublex_done() is called again only via the
                branch (in yylex()) that clears PL_lex_repl, else we'll loop */
        }
        else {
            PL_lex_state = LEX_INTERPCONCAT;
            PL_lex_repl = NULL;
        }
        return ',';
    }
    else {
#ifdef PERL_MAD
        if (PL_madskills) {
            if (PL_thiswhite) {
                if (!PL_endwhite)
                    PL_endwhite = newSVpvs("");
                sv_catsv(PL_endwhite, PL_thiswhite);
                PL_thiswhite = 0;
            }
            if (PL_thistoken)
                sv_setpvs(PL_thistoken,"");
            else
                PL_realtokenstart = -1;
        }
#endif
        LEAVE;
        PL_bufend = SvPVX(PL_linestr);
        PL_bufend += SvCUR(PL_linestr);
        PL_expect = XOPERATOR;
        PL_sublex_info.sub_inwhat = 0;
        return ')';
    }
}

/*
  scan_const

  Extracts the next constant part of a pattern, double-quoted string,
  or transliteration.  This is terrifying code.

  For example, in parsing the double-quoted string "ab\x63$d", it would
  stop at the '$' and return an OP_CONST containing 'abc'.

  It looks at PL_lex_inwhat and PL_lex_inpat to find out whether it's
  processing a pattern (PL_lex_inpat is true), a transliteration
  (PL_lex_inwhat == OP_TRANS is true), or a double-quoted string.

  Returns a pointer to the character scanned up to. If this is
  advanced from the start pointer supplied (i.e. if anything was
  successfully parsed), will leave an OP_CONST for the substring scanned
  in pl_yylval. Caller must intuit reason for not parsing further
  by looking at the next characters herself.

  In patterns:
    expand:
      \N{ABC}  => \N{U+41.42.43}

    pass through:
        all other \-char, including \N and \N{ apart from \N{ABC}

    stops on:
        @ and $ where it appears to be a var, but not for $ as tail anchor
        \l \L \u \U \Q \E
        (?{  or  (??{


  In transliterations:
    characters are VERY literal, except for - not at the start or end
    of the string, which indicates a range. If the range is in bytes,
    scan_const expands the range to the full set of intermediate
    characters. If the range is in utf8, the hyphen is replaced with
    a certain range mark which will be handled by pmtrans() in op.c.

  In double-quoted strings:
    backslashes:
      double-quoted style: \r and \n
      constants: \x31, etc.
      deprecated backrefs: \1 (in substitution replacements)
      case and quoting: \U \Q \E
    stops on @ and $

  scan_const does *not* construct ops to handle interpolated strings.
  It stops processing as soon as it finds an embedded $ or @ variable
  and leaves it to the caller to work out what's going on.

  embedded arrays (whether in pattern or not) could be:
      @foo, @::foo, @'foo, @{foo}, @$foo, @+, @-.

  $ in double-quoted strings must be the symbol of an embedded scalar.

  $ in pattern could be $foo or could be tail anchor.  Assumption:
  it's a tail anchor if $ is the last thing in the string, or if it's
  followed by one of "()| \r\n\t"

  \1 (backreferences) are turned into $1 in substitutions

  The structure of the code is
      while (there's a character to process) {
          handle transliteration ranges
          skip regexp comments /(?#comment)/ and codes /(?{code})/
          skip #-initiated comments in //x patterns
          check for embedded arrays
          check for embedded scalars
          if (backslash) {
              deprecate \1 in substitution replacements
              handle string-changing backslashes \l \U \Q \E, etc.
              switch (what was escaped) {
                  handle \- in a transliteration (becomes a literal -)
                  if a pattern and not \N{, go treat as regular character
                  handle \132 (octal characters)
                  handle \x15 and \x{1234} (hex characters)
                  handle \N{name} (named characters, also \N{3,5} in a pattern)
                  handle \cV (control characters)
                  handle printf-style backslashes (\f, \r, \n, etc)
              } (end switch)
              continue
          } (end if backslash)
          handle regular character
    } (end while character to read)
                
*/

STATIC char *
S_scan_const(pTHX_ char *start)
{
    dVAR;
    register char *send = PL_bufend;            /* end of the constant */
    SV *sv = newSV(send - start);               /* sv for the constant.  See
                                                   note below on sizing. */
    register char *s = start;                   /* start of the constant */
    register char *d = SvPVX(sv);               /* destination for copies */
    bool dorange = FALSE;                       /* are we in a translit range? */
    bool didrange = FALSE;                      /* did we just finish a range? */
    bool in_charclass = FALSE;                  /* within /[...]/ */
    bool has_utf8 = FALSE;                      /* Output constant is UTF8 */
    bool  this_utf8 = cBOOL(UTF);               /* Is the source string assumed
                                                   to be UTF8?  But, this can
                                                   show as true when the source
                                                   isn't utf8, as for example
                                                   when it is entirely composed
                                                   of hex constants */

    /* Note on sizing:  The scanned constant is placed into sv, which is
     * initialized by newSV() assuming one byte of output for every byte of
     * input.  This routine expects newSV() to allocate an extra byte for a
     * trailing NUL, which this routine will append if it gets to the end of
     * the input.  There may be more bytes of input than output (eg., \N{LATIN
     * CAPITAL LETTER A}), or more output than input if the constant ends up
     * recoded to utf8, but each time a construct is found that might increase
     * the needed size, SvGROW() is called.  Its size parameter each time is
     * based on the best guess estimate at the time, namely the length used so
     * far, plus the length the current construct will occupy, plus room for
     * the trailing NUL, plus one byte for every input byte still unscanned */ 

    UV uv;
#ifdef EBCDIC
    UV literal_endpoint = 0;
    bool native_range = TRUE; /* turned to FALSE if the first endpoint is Unicode. */
#endif

    PERL_ARGS_ASSERT_SCAN_CONST;

    assert(PL_lex_inwhat != OP_TRANSR);
    if (PL_lex_inwhat == OP_TRANS && PL_sublex_info.sub_op) {
        /* If we are doing a trans and we know we want UTF8 set expectation */
        has_utf8   = PL_sublex_info.sub_op->op_private & (OPpTRANS_FROM_UTF|OPpTRANS_TO_UTF);
        this_utf8  = PL_sublex_info.sub_op->op_private & (PL_lex_repl ? OPpTRANS_FROM_UTF : OPpTRANS_TO_UTF);
    }


    while (s < send || dorange) {

        /* get transliterations out of the way (they're most literal) */
        if (PL_lex_inwhat == OP_TRANS) {
            /* expand a range A-Z to the full set of characters.  AIE! */
            if (dorange) {
                I32 i;                          /* current expanded character */
                I32 min;                        /* first character in range */
                I32 max;                        /* last character in range */

#ifdef EBCDIC
                UV uvmax = 0;
#endif

                if (has_utf8
#ifdef EBCDIC
                    && !native_range
#endif
                    ) {
                    char * const c = (char*)utf8_hop((U8*)d, -1);
                    char *e = d++;
                    while (e-- > c)
                        *(e + 1) = *e;
                    *c = (char)UTF_TO_NATIVE(0xff);
                    /* mark the range as done, and continue */
                    dorange = FALSE;
                    didrange = TRUE;
                    continue;
                }

                i = d - SvPVX_const(sv);                /* remember current offset */
#ifdef EBCDIC
                SvGROW(sv,
                       SvLEN(sv) + (has_utf8 ?
                                    (512 - UTF_CONTINUATION_MARK +
                                     UNISKIP(0x100))
                                    : 256));
                /* How many two-byte within 0..255: 128 in UTF-8,
                 * 96 in UTF-8-mod. */
#else
                SvGROW(sv, SvLEN(sv) + 256);    /* never more than 256 chars in a range */
#endif
                d = SvPVX(sv) + i;              /* refresh d after realloc */
#ifdef EBCDIC
                if (has_utf8) {
                    int j;
                    for (j = 0; j <= 1; j++) {
                        char * const c = (char*)utf8_hop((U8*)d, -1);
                        const UV uv    = utf8n_to_uvchr((U8*)c, d - c, NULL, 0);
                        if (j)
                            min = (U8)uv;
                        else if (uv < 256)
                            max = (U8)uv;
                        else {
                            max = (U8)0xff; /* only to \xff */
                            uvmax = uv; /* \x{100} to uvmax */
                        }
                        d = c; /* eat endpoint chars */
                     }
                }
               else {
#endif
                   d -= 2;              /* eat the first char and the - */
                   min = (U8)*d;        /* first char in range */
                   max = (U8)d[1];      /* last char in range  */
#ifdef EBCDIC
               }
#endif

                if (min > max) {
                    Perl_croak(aTHX_
                               "Invalid range \"%c-%c\" in transliteration operator",
                               (char)min, (char)max);
                }

#ifdef EBCDIC
                if (literal_endpoint == 2 &&
                    ((isLOWER(min) && isLOWER(max)) ||
                     (isUPPER(min) && isUPPER(max)))) {
                    if (isLOWER(min)) {
                        for (i = min; i <= max; i++)
                            if (isLOWER(i))
                                *d++ = NATIVE_TO_NEED(has_utf8,i);
                    } else {
                        for (i = min; i <= max; i++)
                            if (isUPPER(i))
                                *d++ = NATIVE_TO_NEED(has_utf8,i);
                    }
                }
                else
#endif
                    for (i = min; i <= max; i++)
#ifdef EBCDIC
                        if (has_utf8) {
                            const U8 ch = (U8)NATIVE_TO_UTF(i);
                            if (UNI_IS_INVARIANT(ch))
                                *d++ = (U8)i;
                            else {
                                *d++ = (U8)UTF8_EIGHT_BIT_HI(ch);
                                *d++ = (U8)UTF8_EIGHT_BIT_LO(ch);
                            }
                        }
                        else
#endif
                            *d++ = (char)i;
 
#ifdef EBCDIC
                if (uvmax) {
                    d = (char*)uvchr_to_utf8((U8*)d, 0x100);
                    if (uvmax > 0x101)
                        *d++ = (char)UTF_TO_NATIVE(0xff);
                    if (uvmax > 0x100)
                        d = (char*)uvchr_to_utf8((U8*)d, uvmax);
                }
#endif

                /* mark the range as done, and continue */
                dorange = FALSE;
                didrange = TRUE;
#ifdef EBCDIC
                literal_endpoint = 0;
#endif
                continue;
            }

            /* range begins (ignore - as first or last char) */
            else if (*s == '-' && s+1 < send  && s != start) {
                if (didrange) {
                    Perl_croak(aTHX_ "Ambiguous range in transliteration operator");
                }
                if (has_utf8
#ifdef EBCDIC
                    && !native_range
#endif
                    ) {
                    *d++ = (char)UTF_TO_NATIVE(0xff);   /* use illegal utf8 byte--see pmtrans */
                    s++;
                    continue;
                }
                dorange = TRUE;
                s++;
            }
            else {
                didrange = FALSE;
#ifdef EBCDIC
                literal_endpoint = 0;
                native_range = TRUE;
#endif
            }
        }

        /* if we get here, we're not doing a transliteration */

        else if (*s == '[' && PL_lex_inpat && !in_charclass) {
            char *s1 = s-1;
            int esc = 0;
            while (s1 >= start && *s1-- == '\\')
                esc = !esc;
            if (!esc)
                in_charclass = TRUE;
        }

        else if (*s == ']' && PL_lex_inpat &&  in_charclass) {
            char *s1 = s-1;
            int esc = 0;
            while (s1 >= start && *s1-- == '\\')
                esc = !esc;
            if (!esc)
                in_charclass = FALSE;
        }

        /* skip for regexp comments /(?#comment)/, except for the last
         * char, which will be done separately.
         * Stop on (?{..}) and friends */

        else if (*s == '(' && PL_lex_inpat && s[1] == '?') {
            if (s[2] == '#') {
                while (s+1 < send && *s != ')')
                    *d++ = NATIVE_TO_NEED(has_utf8,*s++);
            }
            else if (!PL_lex_casemods && !in_charclass &&
                     (    s[2] == '{' /* This should match regcomp.c */
                      || (s[2] == '?' && s[3] == '{')))
            {
                break;
            }
        }

        /* likewise skip #-initiated comments in //x patterns */
        else if (*s == '#' && PL_lex_inpat &&
          ((PMOP*)PL_lex_inpat)->op_pmflags & RXf_PMf_EXTENDED) {
            while (s+1 < send && *s != '\n')
                *d++ = NATIVE_TO_NEED(has_utf8,*s++);
        }

        /* no further processing of single-quoted regex */
        else if (PL_lex_inpat && SvIVX(PL_linestr) == '\'')
            goto default_action;

        /* check for embedded arrays
           (@foo, @::foo, @'foo, @{foo}, @$foo, @+, @-)
           */
        else if (*s == '@' && s[1]) {
            if (isALNUM_lazy_if(s+1,UTF))
                break;
            if (strchr(":'{$", s[1]))
                break;
            if (!PL_lex_inpat && (s[1] == '+' || s[1] == '-'))
                break; /* in regexp, neither @+ nor @- are interpolated */
        }

        /* check for embedded scalars.  only stop if we're sure it's a
           variable.
        */
        else if (*s == '$') {
            if (!PL_lex_inpat)  /* not a regexp, so $ must be var */
                break;
            if (s + 1 < send && !strchr("()| \r\n\t", s[1])) {
                if (s[1] == '\\') {
                    Perl_ck_warner(aTHX_ packWARN(WARN_AMBIGUOUS),
                                   "Possible unintended interpolation of $\\ in regex");
                }
                break;          /* in regexp, $ might be tail anchor */
            }
        }

        /* End of else if chain - OP_TRANS rejoin rest */

        /* backslashes */
        if (*s == '\\' && s+1 < send) {
            char* e;    /* Can be used for ending '}', etc. */

            s++;

            /* warn on \1 - \9 in substitution replacements, but note that \11
             * is an octal; and \19 is \1 followed by '9' */
            if (PL_lex_inwhat == OP_SUBST && !PL_lex_inpat &&
                isDIGIT(*s) && *s != '0' && !isDIGIT(s[1]))
            {
                Perl_ck_warner(aTHX_ packWARN(WARN_SYNTAX), "\\%c better written as $%c", *s, *s);
                *--s = '$';
                break;
            }

            /* string-change backslash escapes */
            if (PL_lex_inwhat != OP_TRANS && *s && strchr("lLuUEQF", *s)) {
                --s;
                break;
            }
            /* In a pattern, process \N, but skip any other backslash escapes.
             * This is because we don't want to translate an escape sequence
             * into a meta symbol and have the regex compiler use the meta
             * symbol meaning, e.g. \x{2E} would be confused with a dot.  But
             * in spite of this, we do have to process \N here while the proper
             * charnames handler is in scope.  See bugs #56444 and #62056.
             * There is a complication because \N in a pattern may also stand
             * for 'match a non-nl', and not mean a charname, in which case its
             * processing should be deferred to the regex compiler.  To be a
             * charname it must be followed immediately by a '{', and not look
             * like \N followed by a curly quantifier, i.e., not something like
             * \N{3,}.  regcurly returns a boolean indicating if it is a legal
             * quantifier */
            else if (PL_lex_inpat
                    && (*s != 'N'
                        || s[1] != '{'
                        || regcurly(s + 1)))
            {
                *d++ = NATIVE_TO_NEED(has_utf8,'\\');
                goto default_action;
            }

            switch (*s) {

            /* quoted - in transliterations */
            case '-':
                if (PL_lex_inwhat == OP_TRANS) {
                    *d++ = *s++;
                    continue;
                }
                /* FALL THROUGH */
            default:
                {
                    if ((isALNUMC(*s)))
                        Perl_ck_warner(aTHX_ packWARN(WARN_MISC),
                                       "Unrecognized escape \\%c passed through",
                                       *s);
                    /* default action is to copy the quoted character */
                    goto default_action;
                }

            /* eg. \132 indicates the octal constant 0132 */
            case '0': case '1': case '2': case '3':
            case '4': case '5': case '6': case '7':
                {
                    I32 flags = 0;
                    STRLEN len = 3;
                    uv = NATIVE_TO_UNI(grok_oct(s, &len, &flags, NULL));
                    s += len;
                }
                goto NUM_ESCAPE_INSERT;

            /* eg. \o{24} indicates the octal constant \024 */
            case 'o':
                {
                    STRLEN len;
                    const char* error;

                    bool valid = grok_bslash_o(s, &uv, &len, &error, 1);
                    s += len;
                    if (! valid) {
                        yyerror(error);
                        continue;
                    }
                    goto NUM_ESCAPE_INSERT;
                }

            /* eg. \x24 indicates the hex constant 0x24 */
            case 'x':
                {
                    STRLEN len;
                    const char* error;

                    bool valid = grok_bslash_x(s, &uv, &len, &error, 1);
                    s += len;
                    if (! valid) {
                        yyerror(error);
                        continue;
                    }
                }

              NUM_ESCAPE_INSERT:
                /* Insert oct or hex escaped character.  There will always be
                 * enough room in sv since such escapes will be longer than any
                 * UTF-8 sequence they can end up as, except if they force us
                 * to recode the rest of the string into utf8 */
                
                /* Here uv is the ordinal of the next character being added in
                 * unicode (converted from native). */
                if (!UNI_IS_INVARIANT(uv)) {
                    if (!has_utf8 && uv > 255) {
                        /* Might need to recode whatever we have accumulated so
                         * far if it contains any chars variant in utf8 or
                         * utf-ebcdic. */
                          
                        SvCUR_set(sv, d - SvPVX_const(sv));
                        SvPOK_on(sv);
                        *d = '\0';
                        /* See Note on sizing above.  */
                        sv_utf8_upgrade_flags_grow(sv,
                                        SV_GMAGIC|SV_FORCE_UTF8_UPGRADE,
                                        UNISKIP(uv) + (STRLEN)(send - s) + 1);
                        d = SvPVX(sv) + SvCUR(sv);
                        has_utf8 = TRUE;
                    }

                    if (has_utf8) {
                        d = (char*)uvuni_to_utf8((U8*)d, uv);
                        if (PL_lex_inwhat == OP_TRANS &&
                            PL_sublex_info.sub_op) {
                            PL_sublex_info.sub_op->op_private |=
                                (PL_lex_repl ? OPpTRANS_FROM_UTF
                                             : OPpTRANS_TO_UTF);
                        }
#ifdef EBCDIC
                        if (uv > 255 && !dorange)
                            native_range = FALSE;
#endif
                    }
                    else {
                        *d++ = (char)uv;
                    }
                }
                else {
                    *d++ = (char) uv;
                }
                continue;

            case 'N':
                /* In a non-pattern \N must be a named character, like \N{LATIN
                 * SMALL LETTER A} or \N{U+0041}.  For patterns, it also can
                 * mean to match a non-newline.  For non-patterns, named
                 * characters are converted to their string equivalents. In
                 * patterns, named characters are not converted to their
                 * ultimate forms for the same reasons that other escapes
                 * aren't.  Instead, they are converted to the \N{U+...} form
                 * to get the value from the charnames that is in effect right
                 * now, while preserving the fact that it was a named character
                 * so that the regex compiler knows this */

                /* This section of code doesn't generally use the
                 * NATIVE_TO_NEED() macro to transform the input.  I (khw) did
                 * a close examination of this macro and determined it is a
                 * no-op except on utfebcdic variant characters.  Every
                 * character generated by this that would normally need to be
                 * enclosed by this macro is invariant, so the macro is not
                 * needed, and would complicate use of copy().  XXX There are
                 * other parts of this file where the macro is used
                 * inconsistently, but are saved by it being a no-op */

                /* The structure of this section of code (besides checking for
                 * errors and upgrading to utf8) is:
                 *  Further disambiguate between the two meanings of \N, and if
                 *      not a charname, go process it elsewhere
                 *  If of form \N{U+...}, pass it through if a pattern;
                 *      otherwise convert to utf8
                 *  Otherwise must be \N{NAME}: convert to \N{U+c1.c2...} if a
                 *  pattern; otherwise convert to utf8 */

                /* Here, s points to the 'N'; the test below is guaranteed to
                 * succeed if we are being called on a pattern as we already
                 * know from a test above that the next character is a '{'.
                 * On a non-pattern \N must mean 'named sequence, which
                 * requires braces */
                s++;
                if (*s != '{') {
                    yyerror("Missing braces on \\N{}"); 
                    continue;
                }
                s++;

                /* If there is no matching '}', it is an error. */
                if (! (e = strchr(s, '}'))) {
                    if (! PL_lex_inpat) {
                        yyerror("Missing right brace on \\N{}");
                    } else {
                        yyerror("Missing right brace on \\N{} or unescaped left brace after \\N.");
                    }
                    continue;
                }

                /* Here it looks like a named character */

                if (PL_lex_inpat) {

                    /* XXX This block is temporary code.  \N{} implies that the
                     * pattern is to have Unicode semantics, and therefore
                     * currently has to be encoded in utf8.  By putting it in
                     * utf8 now, we save a whole pass in the regular expression
                     * compiler.  Once that code is changed so Unicode
                     * semantics doesn't necessarily have to be in utf8, this
                     * block should be removed.  However, the code that parses
                     * the output of this would have to be changed to not
                     * necessarily expect utf8 */
                    if (!has_utf8) {
                        SvCUR_set(sv, d - SvPVX_const(sv));
                        SvPOK_on(sv);
                        *d = '\0';
                        /* See Note on sizing above.  */
                        sv_utf8_upgrade_flags_grow(sv,
                                        SV_GMAGIC|SV_FORCE_UTF8_UPGRADE,
                                        /* 5 = '\N{' + cur char + NUL */
                                        (STRLEN)(send - s) + 5);
                        d = SvPVX(sv) + SvCUR(sv);
                        has_utf8 = TRUE;
                    }
                }

                if (*s == 'U' && s[1] == '+') { /* \N{U+...} */
                    I32 flags = PERL_SCAN_ALLOW_UNDERSCORES
                                | PERL_SCAN_DISALLOW_PREFIX;
                    STRLEN len;

                    /* For \N{U+...}, the '...' is a unicode value even on
                     * EBCDIC machines */
                    s += 2;         /* Skip to next char after the 'U+' */
                    len = e - s;
                    uv = grok_hex(s, &len, &flags, NULL);
                    if (len == 0 || len != (STRLEN)(e - s)) {
                        yyerror("Invalid hexadecimal number in \\N{U+...}");
                        s = e + 1;
                        continue;
                    }

                    if (PL_lex_inpat) {

                        /* On non-EBCDIC platforms, pass through to the regex
                         * compiler unchanged.  The reason we evaluated the
                         * number above is to make sure there wasn't a syntax
                         * error.  But on EBCDIC we convert to native so
                         * downstream code can continue to assume it's native
                         */
                        s -= 5;     /* Include the '\N{U+' */
#ifdef EBCDIC
                        d += my_snprintf(d, e - s + 1 + 1,  /* includes the }
                                                               and the \0 */
                                    "\\N{U+%X}",
                                    (unsigned int) UNI_TO_NATIVE(uv));
#else
                        Copy(s, d, e - s + 1, char);    /* 1 = include the } */
                        d += e - s + 1;
#endif
                    }
                    else {  /* Not a pattern: convert the hex to string */

                         /* If destination is not in utf8, unconditionally
                          * recode it to be so.  This is because \N{} implies
                          * Unicode semantics, and scalars have to be in utf8
                          * to guarantee those semantics */
                        if (! has_utf8) {
                            SvCUR_set(sv, d - SvPVX_const(sv));
                            SvPOK_on(sv);
                            *d = '\0';
                            /* See Note on sizing above.  */
                            sv_utf8_upgrade_flags_grow(
                                        sv,
                                        SV_GMAGIC|SV_FORCE_UTF8_UPGRADE,
                                        UNISKIP(uv) + (STRLEN)(send - e) + 1);
                            d = SvPVX(sv) + SvCUR(sv);
                            has_utf8 = TRUE;
                        }

                        /* Add the string to the output */
                        if (UNI_IS_INVARIANT(uv)) {
                            *d++ = (char) uv;
                        }
                        else d = (char*)uvuni_to_utf8((U8*)d, uv);
                    }
                }
                else { /* Here is \N{NAME} but not \N{U+...}. */

                    SV *res;            /* result from charnames */
                    const char *str;    /* the string in 'res' */
                    STRLEN len;         /* its length */

                    /* Get the value for NAME */
                    res = newSVpvn(s, e - s);
                    res = new_constant( NULL, 0, "charnames",
                                        /* includes all of: \N{...} */
                                        res, NULL, s - 3, e - s + 4 );

                    /* Most likely res will be in utf8 already since the
                     * standard charnames uses pack U, but a custom translator
                     * can leave it otherwise, so make sure.  XXX This can be
                     * revisited to not have charnames use utf8 for characters
                     * that don't need it when regexes don't have to be in utf8
                     * for Unicode semantics.  If doing so, remember EBCDIC */
                    sv_utf8_upgrade(res);
                    str = SvPV_const(res, len);

                    /* Don't accept malformed input */
                    if (! is_utf8_string((U8 *) str, len)) {
                        yyerror("Malformed UTF-8 returned by \\N");
                    }
                    else if (PL_lex_inpat) {

                        if (! len) { /* The name resolved to an empty string */
                            Copy("\\N{}", d, 4, char);
                            d += 4;
                        }
                        else {
                            /* In order to not lose information for the regex
                            * compiler, pass the result in the specially made
                            * syntax: \N{U+c1.c2.c3...}, where c1 etc. are
                            * the code points in hex of each character
                            * returned by charnames */

                            const char *str_end = str + len;
                            STRLEN char_length;     /* cur char's byte length */
                            STRLEN output_length;   /* and the number of bytes
                                                       after this is translated
                                                       into hex digits */
                            const STRLEN off = d - SvPVX_const(sv);

                            /* 2 hex per byte; 2 chars for '\N'; 2 chars for
                             * max('U+', '.'); and 1 for NUL */
                            char hex_string[2 * UTF8_MAXBYTES + 5];

                            /* Get the first character of the result. */
                            U32 uv = utf8n_to_uvuni((U8 *) str,
                                                    len,
                                                    &char_length,
                                                    UTF8_ALLOW_ANYUV);

                            /* The call to is_utf8_string() above hopefully
                             * guarantees that there won't be an error.  But
                             * it's easy here to make sure.  The function just
                             * above warns and returns 0 if invalid utf8, but
                             * it can also return 0 if the input is validly a
                             * NUL. Disambiguate */
                            if (uv == 0 && NATIVE_TO_ASCII(*str) != '\0') {
                                uv = UNICODE_REPLACEMENT;
                            }

                            /* Convert first code point to hex, including the
                             * boiler plate before it.  For all these, we
                             * convert to native format so that downstream code
                             * can continue to assume the input is native */
                            output_length =
                                my_snprintf(hex_string, sizeof(hex_string),
                                            "\\N{U+%X",
                                            (unsigned int) UNI_TO_NATIVE(uv));

                            /* Make sure there is enough space to hold it */
                            d = off + SvGROW(sv, off
                                                 + output_length
                                                 + (STRLEN)(send - e)
                                                 + 2);  /* '}' + NUL */
                            /* And output it */
                            Copy(hex_string, d, output_length, char);
                            d += output_length;

                            /* For each subsequent character, append dot and
                             * its ordinal in hex */
                            while ((str += char_length) < str_end) {
                                const STRLEN off = d - SvPVX_const(sv);
                                U32 uv = utf8n_to_uvuni((U8 *) str,
                                                        str_end - str,
                                                        &char_length,
                                                        UTF8_ALLOW_ANYUV);
                                if (uv == 0 && NATIVE_TO_ASCII(*str) != '\0') {
                                    uv = UNICODE_REPLACEMENT;
                                }

                                output_length =
                                    my_snprintf(hex_string, sizeof(hex_string),
                                            ".%X",
                                            (unsigned int) UNI_TO_NATIVE(uv));

                                d = off + SvGROW(sv, off
                                                     + output_length
                                                     + (STRLEN)(send - e)
                                                     + 2);      /* '}' +  NUL */
                                Copy(hex_string, d, output_length, char);
                                d += output_length;
                            }

                            *d++ = '}'; /* Done.  Add the trailing brace */
                        }
                    }
                    else { /* Here, not in a pattern.  Convert the name to a
                            * string. */

                         /* If destination is not in utf8, unconditionally
                          * recode it to be so.  This is because \N{} implies
                          * Unicode semantics, and scalars have to be in utf8
                          * to guarantee those semantics */
                        if (! has_utf8) {
                            SvCUR_set(sv, d - SvPVX_const(sv));
                            SvPOK_on(sv);
                            *d = '\0';
                            /* See Note on sizing above.  */
                            sv_utf8_upgrade_flags_grow(sv,
                                                SV_GMAGIC|SV_FORCE_UTF8_UPGRADE,
                                                len + (STRLEN)(send - s) + 1);
                            d = SvPVX(sv) + SvCUR(sv);
                            has_utf8 = TRUE;
                        } else if (len > (STRLEN)(e - s + 4)) { /* I _guess_ 4 is \N{} --jhi */

                            /* See Note on sizing above.  (NOTE: SvCUR() is not
                             * set correctly here). */
                            const STRLEN off = d - SvPVX_const(sv);
                            d = off + SvGROW(sv, off + len + (STRLEN)(send - s) + 1);
                        }
                        Copy(str, d, len, char);
                        d += len;
                    }
                    SvREFCNT_dec(res);

                    /* Deprecate non-approved name syntax */
                    if (ckWARN_d(WARN_DEPRECATED)) {
                        bool problematic = FALSE;
                        char* i = s;

                        /* For non-ut8 input, look to see that the first
                         * character is an alpha, then loop through the rest
                         * checking that each is a continuation */
                        if (! this_utf8) {
                            if (! isALPHAU(*i)) problematic = TRUE;
                            else for (i = s + 1; i < e; i++) {
                                if (isCHARNAME_CONT(*i)) continue;
                                problematic = TRUE;
                                break;
                            }
                        }
                        else {
                            /* Similarly for utf8.  For invariants can check
                             * directly.  We accept anything above the latin1
                             * range because it is immaterial to Perl if it is
                             * correct or not, and is expensive to check.  But
                             * it is fairly easy in the latin1 range to convert
                             * the variants into a single character and check
                             * those */
                            if (UTF8_IS_INVARIANT(*i)) {
                                if (! isALPHAU(*i)) problematic = TRUE;
                            } else if (UTF8_IS_DOWNGRADEABLE_START(*i)) {
                                if (! isALPHAU(UNI_TO_NATIVE(TWO_BYTE_UTF8_TO_UNI(*i,
                                                                            *(i+1)))))
                                {
                                    problematic = TRUE;
                                }
                            }
                            if (! problematic) for (i = s + UTF8SKIP(s);
                                                    i < e;
                                                    i+= UTF8SKIP(i))
                            {
                                if (UTF8_IS_INVARIANT(*i)) {
                                    if (isCHARNAME_CONT(*i)) continue;
                                } else if (! UTF8_IS_DOWNGRADEABLE_START(*i)) {
                                    continue;
                                } else if (isCHARNAME_CONT(
                                            UNI_TO_NATIVE(
                                            TWO_BYTE_UTF8_TO_UNI(*i, *(i+1)))))
                                {
                                    continue;
                                }
                                problematic = TRUE;
                                break;
                            }
                        }
                        if (problematic) {
                            /* The e-i passed to the final %.*s makes sure that
                             * should the trailing NUL be missing that this
                             * print won't run off the end of the string */
                            Perl_warner(aTHX_ packWARN(WARN_DEPRECATED),
                                        "Deprecated character in \\N{...}; marked by <-- HERE  in \\N{%.*s<-- HERE %.*s",
                                        (int)(i - s + 1), s, (int)(e - i), i + 1);
                        }
                    }
                } /* End \N{NAME} */
#ifdef EBCDIC
                if (!dorange) 
                    native_range = FALSE; /* \N{} is defined to be Unicode */
#endif
                s = e + 1;  /* Point to just after the '}' */
                continue;

            /* \c is a control character */
            case 'c':
                s++;
                if (s < send) {
                    *d++ = grok_bslash_c(*s++, has_utf8, 1);
                }
                else {
                    yyerror("Missing control char name in \\c");
                }
                continue;

            /* printf-style backslashes, formfeeds, newlines, etc */
            case 'b':
                *d++ = NATIVE_TO_NEED(has_utf8,'\b');
                break;
            case 'n':
                *d++ = NATIVE_TO_NEED(has_utf8,'\n');
                break;
            case 'r':
                *d++ = NATIVE_TO_NEED(has_utf8,'\r');
                break;
            case 'f':
                *d++ = NATIVE_TO_NEED(has_utf8,'\f');
                break;
            case 't':
                *d++ = NATIVE_TO_NEED(has_utf8,'\t');
                break;
            case 'e':
                *d++ = ASCII_TO_NEED(has_utf8,'\033');
                break;
            case 'a':
                *d++ = ASCII_TO_NEED(has_utf8,'\007');
                break;
            } /* end switch */

            s++;
            continue;
        } /* end if (backslash) */
#ifdef EBCDIC
        else
            literal_endpoint++;
#endif

    default_action:
        /* If we started with encoded form, or already know we want it,
           then encode the next character */
        if (! NATIVE_IS_INVARIANT((U8)(*s)) && (this_utf8 || has_utf8)) {
            STRLEN len  = 1;


            /* One might think that it is wasted effort in the case of the
             * source being utf8 (this_utf8 == TRUE) to take the next character
             * in the source, convert it to an unsigned value, and then convert
             * it back again.  But the source has not been validated here.  The
             * routine that does the conversion checks for errors like
             * malformed utf8 */

            const UV nextuv   = (this_utf8) ? utf8n_to_uvchr((U8*)s, send - s, &len, 0) : (UV) ((U8) *s);
            const STRLEN need = UNISKIP(NATIVE_TO_UNI(nextuv));
            if (!has_utf8) {
                SvCUR_set(sv, d - SvPVX_const(sv));
                SvPOK_on(sv);
                *d = '\0';
                /* See Note on sizing above.  */
                sv_utf8_upgrade_flags_grow(sv,
                                        SV_GMAGIC|SV_FORCE_UTF8_UPGRADE,
                                        need + (STRLEN)(send - s) + 1);
                d = SvPVX(sv) + SvCUR(sv);
                has_utf8 = TRUE;
            } else if (need > len) {
                /* encoded value larger than old, may need extra space (NOTE:
                 * SvCUR() is not set correctly here).   See Note on sizing
                 * above.  */
                const STRLEN off = d - SvPVX_const(sv);
                d = SvGROW(sv, off + need + (STRLEN)(send - s) + 1) + off;
            }
            s += len;

            d = (char*)uvchr_to_utf8((U8*)d, nextuv);
#ifdef EBCDIC
            if (uv > 255 && !dorange)
                native_range = FALSE;
#endif
        }
        else {
            *d++ = NATIVE_TO_NEED(has_utf8,*s++);
        }
    } /* while loop to process each character */

    /* terminate the string and set up the sv */
    *d = '\0';
    SvCUR_set(sv, d - SvPVX_const(sv));
    if (SvCUR(sv) >= SvLEN(sv))
        Perl_croak(aTHX_ "panic: constant overflowed allocated space, %"UVuf
                   " >= %"UVuf, (UV)SvCUR(sv), (UV)SvLEN(sv));

    SvPOK_on(sv);
    if (PL_encoding && !has_utf8) {
        sv_recode_to_utf8(sv, PL_encoding);
        if (SvUTF8(sv))
            has_utf8 = TRUE;
    }
    if (has_utf8) {
        SvUTF8_on(sv);
        if (PL_lex_inwhat == OP_TRANS && PL_sublex_info.sub_op) {
            PL_sublex_info.sub_op->op_private |=
                    (PL_lex_repl ? OPpTRANS_FROM_UTF : OPpTRANS_TO_UTF);
        }
    }

    /* shrink the sv if we allocated more than we used */
    if (SvCUR(sv) + 5 < SvLEN(sv)) {
        SvPV_shrink_to_cur(sv);
    }

    /* return the substring (via pl_yylval) only if we parsed anything */
    if (s > PL_bufptr) {
        if ( PL_hints & ( PL_lex_inpat ? HINT_NEW_RE : HINT_NEW_STRING ) ) {
            const char *const key = PL_lex_inpat ? "qr" : "q";
            const STRLEN keylen = PL_lex_inpat ? 2 : 1;
            const char *type;
            STRLEN typelen;

            if (PL_lex_inwhat == OP_TRANS) {
                type = "tr";
                typelen = 2;
            } else if (PL_lex_inwhat == OP_SUBST && !PL_lex_inpat) {
                type = "s";
                typelen = 1;
            } else if (PL_lex_inpat && SvIVX(PL_linestr) == '\'') {
                type = "q";
                typelen = 1;
            } else  {
                type = "qq";
                typelen = 2;
            }

            sv = S_new_constant(aTHX_ start, s - start, key, keylen, sv, NULL,
                                type, typelen);
        }
        pl_yylval.opval = (OP*)newSVOP(OP_CONST, 0, sv);
    } else
        SvREFCNT_dec(sv);
    return s;
}

/* S_intuit_more
 * Returns TRUE if there's more to the expression (e.g., a subscript),
 * FALSE otherwise.
 *
 * It deals with "$foo[3]" and /$foo[3]/ and /$foo[0123456789$]+/
 *
 * ->[ and ->{ return TRUE
 * { and [ outside a pattern are always subscripts, so return TRUE
 * if we're outside a pattern and it's not { or [, then return FALSE
 * if we're in a pattern and the first char is a {
 *   {4,5} (any digits around the comma) returns FALSE
 * if we're in a pattern and the first char is a [
 *   [] returns FALSE
 *   [SOMETHING] has a funky algorithm to decide whether it's a
 *      character class or not.  It has to deal with things like
 *      /$foo[-3]/ and /$foo[$bar]/ as well as /$foo[$\d]+/
 * anything else returns TRUE
 */

/* This is the one truly awful dwimmer necessary to conflate C and sed. */

STATIC int
S_intuit_more(pTHX_ register char *s)
{
    dVAR;

    PERL_ARGS_ASSERT_INTUIT_MORE;

    if (PL_lex_brackets)
        return TRUE;
    if (*s == '-' && s[1] == '>' && (s[2] == '[' || s[2] == '{'))
        return TRUE;
    if (*s != '{' && *s != '[')
        return FALSE;
    if (!PL_lex_inpat)
        return TRUE;

    /* In a pattern, so maybe we have {n,m}. */
    if (*s == '{') {
        if (regcurly(s)) {
            return FALSE;
        }
        return TRUE;
    }

    /* On the other hand, maybe we have a character class */

    s++;
    if (*s == ']' || *s == '^')
        return FALSE;
    else {
        /* this is terrifying, and it works */
        int weight = 2;         /* let's weigh the evidence */
        char seen[256];
        unsigned char un_char = 255, last_un_char;
        const char * const send = strchr(s,']');
        char tmpbuf[sizeof PL_tokenbuf * 4];

        if (!send)              /* has to be an expression */
            return TRUE;

        Zero(seen,256,char);
        if (*s == '$')
            weight -= 3;
        else if (isDIGIT(*s)) {
            if (s[1] != ']') {
                if (isDIGIT(s[1]) && s[2] == ']')
                    weight -= 10;
            }
            else
                weight -= 100;
        }
        for (; s < send; s++) {
            last_un_char = un_char;
            un_char = (unsigned char)*s;
            switch (*s) {
            case '@':
            case '&':
            case '$':
                weight -= seen[un_char] * 10;
                if (isALNUM_lazy_if(s+1,UTF)) {
                    int len;
                    scan_ident(s, send, tmpbuf, sizeof tmpbuf, FALSE);
                    len = (int)strlen(tmpbuf);
                    if (len > 1 && gv_fetchpvn_flags(tmpbuf, len,
                                                    UTF ? SVf_UTF8 : 0, SVt_PV))
                        weight -= 100;
                    else
                        weight -= 10;
                }
                else if (*s == '$' && s[1] &&
                  strchr("[#!%*<>()-=",s[1])) {
                    if (/*{*/ strchr("])} =",s[2]))
                        weight -= 10;
                    else
                        weight -= 1;
                }
                break;
            case '\\':
                un_char = 254;
                if (s[1]) {
                    if (strchr("wds]",s[1]))
                        weight += 100;
                    else if (seen[(U8)'\''] || seen[(U8)'"'])
                        weight += 1;
                    else if (strchr("rnftbxcav",s[1]))
                        weight += 40;
                    else if (isDIGIT(s[1])) {
                        weight += 40;
                        while (s[1] && isDIGIT(s[1]))
                            s++;
                    }
                }
                else
                    weight += 100;
                break;
            case '-':
                if (s[1] == '\\')
                    weight += 50;
                if (strchr("aA01! ",last_un_char))
                    weight += 30;
                if (strchr("zZ79~",s[1]))
                    weight += 30;
                if (last_un_char == 255 && (isDIGIT(s[1]) || s[1] == '$'))
                    weight -= 5;        /* cope with negative subscript */
                break;
            default:
                if (!isALNUM(last_un_char)
                    && !(last_un_char == '$' || last_un_char == '@'
                         || last_un_char == '&')
                    && isALPHA(*s) && s[1] && isALPHA(s[1])) {
                    char *d = tmpbuf;
                    while (isALPHA(*s))
                        *d++ = *s++;
                    *d = '\0';
                    if (keyword(tmpbuf, d - tmpbuf, 0))
                        weight -= 150;
                }
                if (un_char == last_un_char + 1)
                    weight += 5;
                weight -= seen[un_char];
                break;
            }
            seen[un_char]++;
        }
        if (weight >= 0)        /* probably a character class */
            return FALSE;
    }

    return TRUE;
}

/*
 * S_intuit_method
 *
 * Does all the checking to disambiguate
 *   foo bar
 * between foo(bar) and bar->foo.  Returns 0 if not a method, otherwise
 * FUNCMETH (bar->foo(args)) or METHOD (bar->foo args).
 *
 * First argument is the stuff after the first token, e.g. "bar".
 *
 * Not a method if foo is a filehandle.
 * Not a method if foo is a subroutine prototyped to take a filehandle.
 * Not a method if it's really "Foo $bar"
 * Method if it's "foo $bar"
 * Not a method if it's really "print foo $bar"
 * Method if it's really "foo package::" (interpreted as package->foo)
 * Not a method if bar is known to be a subroutine ("sub bar; foo bar")
 * Not a method if bar is a filehandle or package, but is quoted with
 *   =>
 */

STATIC int
S_intuit_method(pTHX_ char *start, GV *gv, CV *cv)
{
    dVAR;
    char *s = start + (*start == '$');
    char tmpbuf[sizeof PL_tokenbuf];
    STRLEN len;
    GV* indirgv;
#ifdef PERL_MAD
    int soff;
#endif

    PERL_ARGS_ASSERT_INTUIT_METHOD;

    if (gv && SvTYPE(gv) == SVt_PVGV && GvIO(gv))
            return 0;
    if (cv && SvPOK(cv)) {
                const char *proto = CvPROTO(cv);
                if (proto) {
                    if (*proto == ';')
                        proto++;
                    if (*proto == '*')
                        return 0;
                }
    }
    s = scan_word(s, tmpbuf, sizeof tmpbuf, TRUE, &len);
    /* start is the beginning of the possible filehandle/object,
     * and s is the end of it
     * tmpbuf is a copy of it
     */

    if (*start == '$') {
        if (cv || PL_last_lop_op == OP_PRINT || PL_last_lop_op == OP_SAY ||
                isUPPER(*PL_tokenbuf))
            return 0;
#ifdef PERL_MAD
        len = start - SvPVX(PL_linestr);
#endif
        s = PEEKSPACE(s);
#ifdef PERL_MAD
        start = SvPVX(PL_linestr) + len;
#endif
        PL_bufptr = start;
        PL_expect = XREF;
        return *s == '(' ? FUNCMETH : METHOD;
    }
    if (!keyword(tmpbuf, len, 0)) {
        if (len > 2 && tmpbuf[len - 2] == ':' && tmpbuf[len - 1] == ':') {
            len -= 2;
            tmpbuf[len] = '\0';
#ifdef PERL_MAD
            soff = s - SvPVX(PL_linestr);
#endif
            goto bare_package;
        }
        indirgv = gv_fetchpvn_flags(tmpbuf, len, ( UTF ? SVf_UTF8 : 0 ), SVt_PVCV);
        if (indirgv && GvCVu(indirgv))
            return 0;
        /* filehandle or package name makes it a method */
        if (!cv || GvIO(indirgv) || gv_stashpvn(tmpbuf, len, UTF ? SVf_UTF8 : 0)) {
#ifdef PERL_MAD
            soff = s - SvPVX(PL_linestr);
#endif
            s = PEEKSPACE(s);
            if ((PL_bufend - s) >= 2 && *s == '=' && *(s+1) == '>')
                return 0;       /* no assumptions -- "=>" quotes bareword */
      bare_package:
            start_force(PL_curforce);
            NEXTVAL_NEXTTOKE.opval = (OP*)newSVOP(OP_CONST, 0,
                                                  S_newSV_maybe_utf8(aTHX_ tmpbuf, len));
            NEXTVAL_NEXTTOKE.opval->op_private = OPpCONST_BARE;
            if (PL_madskills)
                curmad('X', newSVpvn_flags(start,SvPVX(PL_linestr) + soff - start,
                                                            ( UTF ? SVf_UTF8 : 0 )));
            PL_expect = XTERM;
            force_next(WORD);
            PL_bufptr = s;
#ifdef PERL_MAD
            PL_bufptr = SvPVX(PL_linestr) + soff; /* restart before space */
#endif
            return *s == '(' ? FUNCMETH : METHOD;
        }
    }
    return 0;
}

/* Encoded script support. filter_add() effectively inserts a
 * 'pre-processing' function into the current source input stream.
 * Note that the filter function only applies to the current source file
 * (e.g., it will not affect files 'require'd or 'use'd by this one).
 *
 * The datasv parameter (which may be NULL) can be used to pass
 * private data to this instance of the filter. The filter function
 * can recover the SV using the FILTER_DATA macro and use it to
 * store private buffers and state information.
 *
 * The supplied datasv parameter is upgraded to a PVIO type
 * and the IoDIRP/IoANY field is used to store the function pointer,
 * and IOf_FAKE_DIRP is enabled on datasv to mark this as such.
 * Note that IoTOP_NAME, IoFMT_NAME, IoBOTTOM_NAME, if set for
 * private use must be set using malloc'd pointers.
 */

SV *
Perl_filter_add(pTHX_ filter_t funcp, SV *datasv)
{
    dVAR;
    if (!funcp)
        return NULL;

    if (!PL_parser)
        return NULL;

    if (PL_parser->lex_flags & LEX_IGNORE_UTF8_HINTS)
        Perl_croak(aTHX_ "Source filters apply only to byte streams");

    if (!PL_rsfp_filters)
        PL_rsfp_filters = newAV();
    if (!datasv)
        datasv = newSV(0);
    SvUPGRADE(datasv, SVt_PVIO);
    IoANY(datasv) = FPTR2DPTR(void *, funcp); /* stash funcp into spare field */
    IoFLAGS(datasv) |= IOf_FAKE_DIRP;
    DEBUG_P(PerlIO_printf(Perl_debug_log, "filter_add func %p (%s)\n",
                          FPTR2DPTR(void *, IoANY(datasv)),
                          SvPV_nolen(datasv)));
    av_unshift(PL_rsfp_filters, 1);
    av_store(PL_rsfp_filters, 0, datasv) ;
    if (
        !PL_parser->filtered
     && PL_parser->lex_flags & LEX_EVALBYTES
     && PL_bufptr < PL_bufend
    ) {
        const char *s = PL_bufptr;
        while (s < PL_bufend) {
            if (*s == '\n') {
                SV *linestr = PL_parser->linestr;
                char *buf = SvPVX(linestr);
                STRLEN const bufptr_pos = PL_parser->bufptr - buf;
                STRLEN const oldbufptr_pos = PL_parser->oldbufptr - buf;
                STRLEN const oldoldbufptr_pos=PL_parser->oldoldbufptr-buf;
                STRLEN const linestart_pos = PL_parser->linestart - buf;
                STRLEN const last_uni_pos =
                    PL_parser->last_uni ? PL_parser->last_uni - buf : 0;
                STRLEN const last_lop_pos =
                    PL_parser->last_lop ? PL_parser->last_lop - buf : 0;
                av_push(PL_rsfp_filters, linestr);
                PL_parser->linestr = 
                    newSVpvn(SvPVX(linestr), ++s-SvPVX(linestr));
                buf = SvPVX(PL_parser->linestr);
                PL_parser->bufend = buf + SvCUR(PL_parser->linestr);
                PL_parser->bufptr = buf + bufptr_pos;
                PL_parser->oldbufptr = buf + oldbufptr_pos;
                PL_parser->oldoldbufptr = buf + oldoldbufptr_pos;
                PL_parser->linestart = buf + linestart_pos;
                if (PL_parser->last_uni)
                    PL_parser->last_uni = buf + last_uni_pos;
                if (PL_parser->last_lop)
                    PL_parser->last_lop = buf + last_lop_pos;
                SvLEN(linestr) = SvCUR(linestr);
                SvCUR(linestr) = s-SvPVX(linestr);
                PL_parser->filtered = 1;
                break;
            }
            s++;
        }
    }
    return(datasv);
}


/* Delete most recently added instance of this filter function. */
void
Perl_filter_del(pTHX_ filter_t funcp)
{
    dVAR;
    SV *datasv;

    PERL_ARGS_ASSERT_FILTER_DEL;

#ifdef DEBUGGING
    DEBUG_P(PerlIO_printf(Perl_debug_log, "filter_del func %p",
                          FPTR2DPTR(void*, funcp)));
#endif
    if (!PL_parser || !PL_rsfp_filters || AvFILLp(PL_rsfp_filters)<0)
        return;
    /* if filter is on top of stack (usual case) just pop it off */
    datasv = FILTER_DATA(AvFILLp(PL_rsfp_filters));
    if (IoANY(datasv) == FPTR2DPTR(void *, funcp)) {
        sv_free(av_pop(PL_rsfp_filters));

        return;
    }
    /* we need to search for the correct entry and clear it     */
    Perl_die(aTHX_ "filter_del can only delete in reverse order (currently)");
}


/* Invoke the idxth filter function for the current rsfp.        */
/* maxlen 0 = read one text line */
I32
Perl_filter_read(pTHX_ int idx, SV *buf_sv, int maxlen)
{
    dVAR;
    filter_t funcp;
    SV *datasv = NULL;
    /* This API is bad. It should have been using unsigned int for maxlen.
       Not sure if we want to change the API, but if not we should sanity
       check the value here.  */
    unsigned int correct_length
        = maxlen < 0 ?
#ifdef PERL_MICRO
        0x7FFFFFFF
#else
        INT_MAX
#endif
        : maxlen;

    PERL_ARGS_ASSERT_FILTER_READ;

    if (!PL_parser || !PL_rsfp_filters)
        return -1;
    if (idx > AvFILLp(PL_rsfp_filters)) {       /* Any more filters?    */
        /* Provide a default input filter to make life easy.    */
        /* Note that we append to the line. This is handy.      */
        DEBUG_P(PerlIO_printf(Perl_debug_log,
                              "filter_read %d: from rsfp\n", idx));
        if (correct_length) {
            /* Want a block */
            int len ;
            const int old_len = SvCUR(buf_sv);

            /* ensure buf_sv is large enough */
            SvGROW(buf_sv, (STRLEN)(old_len + correct_length + 1)) ;
            if ((len = PerlIO_read(PL_rsfp, SvPVX(buf_sv) + old_len,
                                   correct_length)) <= 0) {
                if (PerlIO_error(PL_rsfp))
                    return -1;          /* error */
                else
                    return 0 ;          /* end of file */
            }
            SvCUR_set(buf_sv, old_len + len) ;
            SvPVX(buf_sv)[old_len + len] = '\0';
        } else {
            /* Want a line */
            if (sv_gets(buf_sv, PL_rsfp, SvCUR(buf_sv)) == NULL) {
                if (PerlIO_error(PL_rsfp))
                    return -1;          /* error */
                else
                    return 0 ;          /* end of file */
            }
        }
        return SvCUR(buf_sv);
    }
    /* Skip this filter slot if filter has been deleted */
    if ( (datasv = FILTER_DATA(idx)) == &PL_sv_undef) {
        DEBUG_P(PerlIO_printf(Perl_debug_log,
                              "filter_read %d: skipped (filter deleted)\n",
                              idx));
        return FILTER_READ(idx+1, buf_sv, correct_length); /* recurse */
    }
    if (SvTYPE(datasv) != SVt_PVIO) {
        if (correct_length) {
            /* Want a block */
            const STRLEN remainder = SvLEN(datasv) - SvCUR(datasv);
            if (!remainder) return 0; /* eof */
            if (correct_length > remainder) correct_length = remainder;
            sv_catpvn(buf_sv, SvEND(datasv), correct_length);
            SvCUR_set(datasv, SvCUR(datasv) + correct_length);
        } else {
            /* Want a line */
            const char *s = SvEND(datasv);
            const char *send = SvPVX(datasv) + SvLEN(datasv);
            while (s < send) {
                if (*s == '\n') {
                    s++;
                    break;
                }
                s++;
            }
            if (s == send) return 0; /* eof */
            sv_catpvn(buf_sv, SvEND(datasv), s-SvEND(datasv));
            SvCUR_set(datasv, s-SvPVX(datasv));
        }
        return SvCUR(buf_sv);
    }
    /* Get function pointer hidden within datasv        */
    funcp = DPTR2FPTR(filter_t, IoANY(datasv));
    DEBUG_P(PerlIO_printf(Perl_debug_log,
                          "filter_read %d: via function %p (%s)\n",
                          idx, (void*)datasv, SvPV_nolen_const(datasv)));
    /* Call function. The function is expected to       */
    /* call "FILTER_READ(idx+1, buf_sv)" first.         */
    /* Return: <0:error, =0:eof, >0:not eof             */
    return (*funcp)(aTHX_ idx, buf_sv, correct_length);
}

STATIC char *
S_filter_gets(pTHX_ register SV *sv, STRLEN append)
{
    dVAR;

    PERL_ARGS_ASSERT_FILTER_GETS;

#ifdef PERL_CR_FILTER
    if (!PL_rsfp_filters) {
        filter_add(S_cr_textfilter,NULL);
    }
#endif
    if (PL_rsfp_filters) {
        if (!append)
            SvCUR_set(sv, 0);   /* start with empty line        */
        if (FILTER_READ(0, sv, 0) > 0)
            return ( SvPVX(sv) ) ;
        else
            return NULL ;
    }
    else
        return (sv_gets(sv, PL_rsfp, append));
}

STATIC HV *
S_find_in_my_stash(pTHX_ const char *pkgname, STRLEN len)
{
    dVAR;
    GV *gv;

    PERL_ARGS_ASSERT_FIND_IN_MY_STASH;

    if (len == 11 && *pkgname == '_' && strEQ(pkgname, "__PACKAGE__"))
        return PL_curstash;

    if (len > 2 &&
        (pkgname[len - 2] == ':' && pkgname[len - 1] == ':') &&
        (gv = gv_fetchpvn_flags(pkgname, len, ( UTF ? SVf_UTF8 : 0 ), SVt_PVHV)))
    {
        return GvHV(gv);                        /* Foo:: */
    }

    /* use constant CLASS => 'MyClass' */
    gv = gv_fetchpvn_flags(pkgname, len, UTF ? SVf_UTF8 : 0, SVt_PVCV);
    if (gv && GvCV(gv)) {
        SV * const sv = cv_const_sv(GvCV(gv));
        if (sv)
            pkgname = SvPV_const(sv, len);
    }

    return gv_stashpvn(pkgname, len, UTF ? SVf_UTF8 : 0);
}

/*
 * S_readpipe_override
 * Check whether readpipe() is overridden, and generates the appropriate
 * optree, provided sublex_start() is called afterwards.
 */
STATIC void
S_readpipe_override(pTHX)
{
    GV **gvp;
    GV *gv_readpipe = gv_fetchpvs("readpipe", GV_NOTQUAL, SVt_PVCV);
    pl_yylval.ival = OP_BACKTICK;
    if ((gv_readpipe
                && GvCVu(gv_readpipe) && GvIMPORTED_CV(gv_readpipe))
            ||
            ((gvp = (GV**)hv_fetchs(PL_globalstash, "readpipe", FALSE))
             && (gv_readpipe = *gvp) && isGV_with_GP(gv_readpipe)
             && GvCVu(gv_readpipe) && GvIMPORTED_CV(gv_readpipe)))
    {
        PL_lex_op = (OP*)newUNOP(OP_ENTERSUB, OPf_STACKED,
            op_append_elem(OP_LIST,
                newSVOP(OP_CONST, 0, &PL_sv_undef), /* value will be read later */
                newCVREF(0, newGVOP(OP_GV, 0, gv_readpipe))));
    }
}

#ifdef PERL_MAD 
 /*
 * Perl_madlex
 * The intent of this yylex wrapper is to minimize the changes to the
 * tokener when we aren't interested in collecting madprops.  It remains
 * to be seen how successful this strategy will be...
 */

int
Perl_madlex(pTHX)
{
    int optype;
    char *s = PL_bufptr;

    /* make sure PL_thiswhite is initialized */
    PL_thiswhite = 0;
    PL_thismad = 0;

    /* just do what yylex would do on pending identifier; leave PL_thiswhite alone */
    if (PL_lex_state != LEX_KNOWNEXT && PL_pending_ident)
        return S_pending_ident(aTHX);

    /* previous token ate up our whitespace? */
    if (!PL_lasttoke && PL_nextwhite) {
        PL_thiswhite = PL_nextwhite;
        PL_nextwhite = 0;
    }

    /* isolate the token, and figure out where it is without whitespace */
    PL_realtokenstart = -1;
    PL_thistoken = 0;
    optype = yylex();
    s = PL_bufptr;
    assert(PL_curforce < 0);

    if (!PL_thismad || PL_thismad->mad_key == '^') {    /* not forced already? */
        if (!PL_thistoken) {
            if (PL_realtokenstart < 0 || !CopLINE(PL_curcop))
                PL_thistoken = newSVpvs("");
            else {
                char * const tstart = SvPVX(PL_linestr) + PL_realtokenstart;
                PL_thistoken = newSVpvn(tstart, s - tstart);
            }
        }
        if (PL_thismad) /* install head */
            CURMAD('X', PL_thistoken);
    }

    /* last whitespace of a sublex? */
    if (optype == ')' && PL_endwhite) {
        CURMAD('X', PL_endwhite);
    }

    if (!PL_thismad) {

        /* if no whitespace and we're at EOF, bail.  Otherwise fake EOF below. */
        if (!PL_thiswhite && !PL_endwhite && !optype) {
            sv_free(PL_thistoken);
            PL_thistoken = 0;
            return 0;
        }

        /* put off final whitespace till peg */
        if (optype == ';' && !PL_rsfp && !PL_parser->filtered) {
            PL_nextwhite = PL_thiswhite;
            PL_thiswhite = 0;
        }
        else if (PL_thisopen) {
            CURMAD('q', PL_thisopen);
            if (PL_thistoken)
                sv_free(PL_thistoken);
            PL_thistoken = 0;
        }
        else {
            /* Store actual token text as madprop X */
            CURMAD('X', PL_thistoken);
        }

        if (PL_thiswhite) {
            /* add preceding whitespace as madprop _ */
            CURMAD('_', PL_thiswhite);
        }

        if (PL_thisstuff) {
            /* add quoted material as madprop = */
            CURMAD('=', PL_thisstuff);
        }

        if (PL_thisclose) {
            /* add terminating quote as madprop Q */
            CURMAD('Q', PL_thisclose);
        }
    }

    /* special processing based on optype */

    switch (optype) {

    /* opval doesn't need a TOKEN since it can already store mp */
    case WORD:
    case METHOD:
    case FUNCMETH:
    case THING:
    case PMFUNC:
    case PRIVATEREF:
    case FUNC0SUB:
    case UNIOPSUB:
    case LSTOPSUB:
    case LABEL:
        if (pl_yylval.opval)
            append_madprops(PL_thismad, pl_yylval.opval, 0);
        PL_thismad = 0;
        return optype;

    /* fake EOF */
    case 0:
        optype = PEG;
        if (PL_endwhite) {
            addmad(newMADsv('p', PL_endwhite), &PL_thismad, 0);
            PL_endwhite = 0;
        }
        break;

    case ']':
    case '}':
        if (PL_faketokens)
            break;
        /* remember any fake bracket that lexer is about to discard */ 
        if (PL_lex_brackets == 1 &&
            ((expectation)PL_lex_brackstack[0] & XFAKEBRACK))
        {
            s = PL_bufptr;
            while (s < PL_bufend && (*s == ' ' || *s == '\t'))
                s++;
            if (*s == '}') {
                PL_thiswhite = newSVpvn(PL_bufptr, ++s - PL_bufptr);
                addmad(newMADsv('#', PL_thiswhite), &PL_thismad, 0);
                PL_thiswhite = 0;
                PL_bufptr = s - 1;
                break;  /* don't bother looking for trailing comment */
            }
            else
                s = PL_bufptr;
        }
        if (optype == ']')
            break;
        /* FALLTHROUGH */

    /* attach a trailing comment to its statement instead of next token */
    case ';':
        if (PL_faketokens)
            break;
        if (PL_bufptr > PL_oldbufptr && PL_bufptr[-1] == optype) {
            s = PL_bufptr;
            while (s < PL_bufend && (*s == ' ' || *s == '\t'))
                s++;
            if (*s == '\n' || *s == '#') {
                while (s < PL_bufend && *s != '\n')
                    s++;
                if (s < PL_bufend)
                    s++;
                PL_thiswhite = newSVpvn(PL_bufptr, s - PL_bufptr);
                addmad(newMADsv('#', PL_thiswhite), &PL_thismad, 0);
                PL_thiswhite = 0;
                PL_bufptr = s;
            }
        }
        break;

    /* ival */
    default:
        break;

    }

    /* Create new token struct.  Note: opvals return early above. */
    pl_yylval.tkval = newTOKEN(optype, pl_yylval, PL_thismad);
    PL_thismad = 0;
    return optype;
}
#endif

STATIC char *
S_tokenize_use(pTHX_ int is_use, char *s) {
    dVAR;

    PERL_ARGS_ASSERT_TOKENIZE_USE;

    if (PL_expect != XSTATE)
        yyerror(Perl_form(aTHX_ "\"%s\" not allowed in expression",
                    is_use ? "use" : "no"));
    PL_expect = XTERM;
    s = SKIPSPACE1(s);
    if (isDIGIT(*s) || (*s == 'v' && isDIGIT(s[1]))) {
        s = force_version(s, TRUE);
        if (*s == ';' || *s == '}'
                || (s = SKIPSPACE1(s), (*s == ';' || *s == '}'))) {
            start_force(PL_curforce);
            NEXTVAL_NEXTTOKE.opval = NULL;
            force_next(WORD);
        }
        else if (*s == 'v') {
            s = force_word(s,WORD,FALSE,TRUE,FALSE);
            s = force_version(s, FALSE);
        }
    }
    else {
        s = force_word(s,WORD,FALSE,TRUE,FALSE);
        s = force_version(s, FALSE);
    }
    pl_yylval.ival = is_use;
    return s;
}
#ifdef DEBUGGING
    static const char* const exp_name[] =
        { "OPERATOR", "TERM", "REF", "STATE", "BLOCK", "ATTRBLOCK",
          "ATTRTERM", "TERMBLOCK", "TERMORDORDOR"
        };
#endif

#define word_takes_any_delimeter(p,l) S_word_takes_any_delimeter(p,l)
STATIC bool
S_word_takes_any_delimeter(char *p, STRLEN len)
{
    return (len == 1 && strchr("msyq", p[0])) ||
           (len == 2 && (
            (p[0] == 't' && p[1] == 'r') ||
            (p[0] == 'q' && strchr("qwxr", p[1]))));
}

/*
  yylex

  Works out what to call the token just pulled out of the input
  stream.  The yacc parser takes care of taking the ops we return and
  stitching them into a tree.

  Returns:
    PRIVATEREF

  Structure:
      if read an identifier
          if we're in a my declaration
              croak if they tried to say my($foo::bar)
              build the ops for a my() declaration
          if it's an access to a my() variable
              are we in a sort block?
                  croak if my($a); $a <=> $b
              build ops for access to a my() variable
          if in a dq string, and they've said @foo and we can't find @foo
              croak
          build ops for a bareword
      if we already built the token before, use it.
*/


#ifdef __SC__
#pragma segment Perl_yylex
#endif
int
Perl_yylex(pTHX)
{
    dVAR;
    register char *s = PL_bufptr;
    register char *d;
    STRLEN len;
    bool bof = FALSE, formbrack = FALSE;
    U32 fake_eof = 0;

    /* orig_keyword, gvp, and gv are initialized here because
     * jump to the label just_a_word_zero can bypass their
     * initialization later. */
    I32 orig_keyword = 0;
    GV *gv = NULL;
    GV **gvp = NULL;

    DEBUG_T( {
        SV* tmp = newSVpvs("");
        PerlIO_printf(Perl_debug_log, "### %"IVdf":LEX_%s/X%s %s\n",
            (IV)CopLINE(PL_curcop),
            lex_state_names[PL_lex_state],
            exp_name[PL_expect],
            pv_display(tmp, s, strlen(s), 0, 60));
        SvREFCNT_dec(tmp);
    } );
    /* check if there's an identifier for us to look at */
    if (PL_lex_state != LEX_KNOWNEXT && PL_pending_ident)
        return REPORT(S_pending_ident(aTHX));

    /* no identifier pending identification */

    switch (PL_lex_state) {
#ifdef COMMENTARY
    case LEX_NORMAL:            /* Some compilers will produce faster */
    case LEX_INTERPNORMAL:      /* code if we comment these out. */
        break;
#endif

    /* when we've already built the next token, just pull it out of the queue */
    case LEX_KNOWNEXT:
#ifdef PERL_MAD
        PL_lasttoke--;
        pl_yylval = PL_nexttoke[PL_lasttoke].next_val;
        if (PL_madskills) {
            PL_thismad = PL_nexttoke[PL_lasttoke].next_mad;
            PL_nexttoke[PL_lasttoke].next_mad = 0;
            if (PL_thismad && PL_thismad->mad_key == '_') {
                PL_thiswhite = MUTABLE_SV(PL_thismad->mad_val);
                PL_thismad->mad_val = 0;
                mad_free(PL_thismad);
                PL_thismad = 0;
            }
        }
        if (!PL_lasttoke) {
            PL_lex_state = PL_lex_defer;
            PL_expect = PL_lex_expect;
            PL_lex_defer = LEX_NORMAL;
            if (!PL_nexttoke[PL_lasttoke].next_type)
                return yylex();
        }
#else
        PL_nexttoke--;
        pl_yylval = PL_nextval[PL_nexttoke];
      &n