Commit | Line | Data |
---|---|---|
3ed9f206 JH |
1 | package Switch; |
2 | ||
3 | use strict; | |
4 | use vars qw($VERSION); | |
5 | use Carp; | |
6 | ||
d38ca171 | 7 | $VERSION = '2.06'; |
3ed9f206 JH |
8 | |
9 | ||
10 | # LOAD FILTERING MODULE... | |
11 | use Filter::Util::Call; | |
12 | ||
13 | sub __(); | |
14 | ||
15 | # CATCH ATTEMPTS TO CALL case OUTSIDE THE SCOPE OF ANY switch | |
16 | ||
74a6a946 | 17 | $::_S_W_I_T_C_H = sub { croak "case/when statement not in switch/given block" }; |
3ed9f206 JH |
18 | |
19 | my $offset; | |
20 | my $fallthrough; | |
74a6a946 | 21 | my ($Perl5, $Perl6) = (0,0); |
3ed9f206 JH |
22 | |
23 | sub import | |
24 | { | |
3961318e | 25 | $DB::single = 1; |
3ed9f206 JH |
26 | $fallthrough = grep /\bfallthrough\b/, @_; |
27 | $offset = (caller)[2]+1; | |
a1813bef | 28 | filter_add({}) unless @_>1 && $_[1] eq 'noimport'; |
3ed9f206 JH |
29 | my $pkg = caller; |
30 | no strict 'refs'; | |
31 | for ( qw( on_defined on_exists ) ) | |
32 | { | |
33 | *{"${pkg}::$_"} = \&$_; | |
34 | } | |
35 | *{"${pkg}::__"} = \&__ if grep /__/, @_; | |
74a6a946 JH |
36 | $Perl6 = 1 if grep(/Perl\s*6/i, @_); |
37 | $Perl5 = 1 if grep(/Perl\s*5/i, @_) || !grep(/Perl\s*6/i, @_); | |
3ed9f206 JH |
38 | 1; |
39 | } | |
40 | ||
41 | sub unimport | |
42 | { | |
43 | filter_del() | |
44 | } | |
45 | ||
46 | sub filter | |
47 | { | |
48 | my($self) = @_ ; | |
49 | local $Switch::file = (caller)[1]; | |
50 | ||
51 | my $status = 1; | |
52 | $status = filter_read(10_000); | |
53 | return $status if $status<0; | |
54 | $_ = filter_blocks($_,$offset); | |
55 | $_ = "# line $offset\n" . $_ if $offset; undef $offset; | |
56 | # print STDERR $_; | |
57 | return $status; | |
58 | } | |
59 | ||
60 | use Text::Balanced ':ALL'; | |
61 | ||
62 | sub line | |
63 | { | |
64 | my ($pretext,$offset) = @_; | |
74a6a946 | 65 | ($pretext=~tr/\n/\n/)+($offset||0); |
3ed9f206 JH |
66 | } |
67 | ||
68 | sub is_block | |
69 | { | |
70 | local $SIG{__WARN__}=sub{die$@}; | |
71 | local $^W=1; | |
72 | my $ishash = defined eval 'my $hr='.$_[0]; | |
73 | undef $@; | |
74 | return !$ishash; | |
75 | } | |
76 | ||
d38ca171 JH |
77 | |
78 | my $EOP = qr/\n\n|\Z/; | |
79 | my $CUT = qr/\n=cut.*$EOP/; | |
80 | my $pod_or_DATA = qr/ ^=(?:head[1-4]|item) .*? $CUT | |
81 | | ^=pod .*? $CUT | |
82 | | ^=for .*? $EOP | |
83 | | ^=begin \s* (\S+) .*? \n=end \s* \1 .*? $EOP | |
84 | | ^__(DATA|END)__\n.* | |
85 | /smx; | |
86 | ||
3ed9f206 JH |
87 | my $casecounter = 1; |
88 | sub filter_blocks | |
89 | { | |
90 | my ($source, $line) = @_; | |
74a6a946 JH |
91 | return $source unless $Perl5 && $source =~ /case|switch/ |
92 | || $Perl6 && $source =~ /when|given/; | |
3ed9f206 JH |
93 | pos $source = 0; |
94 | my $text = ""; | |
95 | component: while (pos $source < length $source) | |
96 | { | |
3961318e | 97 | if ($source =~ m/(\G\s*use\s+Switch\b)/gc) |
3ed9f206 JH |
98 | { |
99 | $text .= q{use Switch 'noimport'}; | |
100 | next component; | |
101 | } | |
d38ca171 | 102 | my @pos = Text::Balanced::_match_quotelike(\$source,qr/\s*/,1,0); |
3ed9f206 JH |
103 | if (defined $pos[0]) |
104 | { | |
3961318e | 105 | $text .= " " . substr($source,$pos[2],$pos[18]-$pos[2]); |
3ed9f206 JH |
106 | next component; |
107 | } | |
d38ca171 JH |
108 | if ($source =~ m/\G\s*($pod_or_DATA)/gc) { |
109 | next component; | |
110 | } | |
3ed9f206 JH |
111 | @pos = Text::Balanced::_match_variable(\$source,qr/\s*/); |
112 | if (defined $pos[0]) | |
113 | { | |
3961318e | 114 | $text .= " " . substr($source,$pos[0],$pos[4]-$pos[0]); |
3ed9f206 JH |
115 | next component; |
116 | } | |
117 | ||
74a6a946 JH |
118 | if ($Perl5 && $source =~ m/\G(\n*)(\s*)(switch)\b(?=\s*[(])/gc |
119 | || $Perl6 && $source =~ m/\G(\n*)(\s*)(given)\b(?=\s*[(])/gc) | |
3ed9f206 | 120 | { |
74a6a946 | 121 | my $keyword = $3; |
3ed9f206 | 122 | $text .= $1.$2.'S_W_I_T_C_H: while (1) '; |
3961318e | 123 | @pos = Text::Balanced::_match_codeblock(\$source,qr/\s*/,qr/\(/,qr/\)/,qr/[[{(<]/,qr/[]})>]/,undef) |
3ed9f206 | 124 | or do { |
74a6a946 | 125 | die "Bad $keyword statement (problem in the parentheses?) near $Switch::file line ", line(substr($source,0,pos $source),$line), "\n"; |
3ed9f206 JH |
126 | }; |
127 | my $arg = filter_blocks(substr($source,$pos[0],$pos[4]-$pos[0]),line(substr($source,0,$pos[0]),$line)); | |
128 | $arg =~ s {^\s*[(]\s*%} { ( \\\%} || | |
129 | $arg =~ s {^\s*[(]\s*m\b} { ( qr} || | |
130 | $arg =~ s {^\s*[(]\s*/} { ( qr/} || | |
131 | $arg =~ s {^\s*[(]\s*qw} { ( \\qw}; | |
132 | @pos = Text::Balanced::_match_codeblock(\$source,qr/\s*/,qr/\{/,qr/\}/,qr/\{/,qr/\}/,undef) | |
133 | or do { | |
74a6a946 | 134 | die "Bad $keyword statement (problem in the code block?) near $Switch::file line ", line(substr($source,0, pos $source), $line), "\n"; |
3ed9f206 JH |
135 | }; |
136 | my $code = filter_blocks(substr($source,$pos[0],$pos[4]-$pos[0]),line(substr($source,0,$pos[0]),$line)); | |
137 | $code =~ s/{/{ local \$::_S_W_I_T_C_H; Switch::switch $arg;/; | |
138 | $text .= $code . 'continue {last}'; | |
139 | next component; | |
140 | } | |
74a6a946 JH |
141 | elsif ($Perl5 && $source =~ m/\G(\s*)(case\b)(?!\s*=>)/gc |
142 | || $Perl6 && $source =~ m/\G(\s*)(when\b)(?!\s*=>)/gc) | |
3ed9f206 | 143 | { |
74a6a946 | 144 | my $keyword = $2; |
3ed9f206 JH |
145 | $text .= $1."if (Switch::case"; |
146 | if (@pos = Text::Balanced::_match_codeblock(\$source,qr/\s*/,qr/\{/,qr/\}/,qr/\{/,qr/\}/,undef)) { | |
147 | my $code = substr($source,$pos[0],$pos[4]-$pos[0]); | |
148 | $text .= " sub" if is_block $code; | |
149 | $text .= " " . filter_blocks($code,line(substr($source,0,$pos[0]),$line)) . ")"; | |
150 | } | |
151 | elsif (@pos = Text::Balanced::_match_codeblock(\$source,qr/\s*/,qr/[[(]/,qr/[])]/,qr/[[({]/,qr/[])}]/,undef)) { | |
152 | my $code = filter_blocks(substr($source,$pos[0],$pos[4]-$pos[0]),line(substr($source,0,$pos[0]),$line)); | |
153 | $code =~ s {^\s*[(]\s*%} { ( \\\%} || | |
154 | $code =~ s {^\s*[(]\s*m\b} { ( qr} || | |
155 | $code =~ s {^\s*[(]\s*/} { ( qr/} || | |
156 | $code =~ s {^\s*[(]\s*qw} { ( \\qw}; | |
157 | $text .= " $code)"; | |
158 | } | |
74a6a946 JH |
159 | elsif ($Perl6 && do{@pos = Text::Balanced::_match_variable(\$source,qr/\s*/)}) { |
160 | my $code = filter_blocks(substr($source,$pos[0],$pos[4]-$pos[0]),line(substr($source,0,$pos[0]),$line)); | |
161 | $code =~ s {^\s*%} { \%} || | |
162 | $code =~ s {^\s*@} { \@}; | |
163 | $text .= " $code)"; | |
164 | } | |
d38ca171 | 165 | elsif ( @pos = Text::Balanced::_match_quotelike(\$source,qr/\s*/,1,0)) { |
3ed9f206 JH |
166 | my $code = substr($source,$pos[2],$pos[18]-$pos[2]); |
167 | $code = filter_blocks($code,line(substr($source,0,$pos[2]),$line)); | |
168 | $code =~ s {^\s*m} { qr} || | |
169 | $code =~ s {^\s*/} { qr/} || | |
170 | $code =~ s {^\s*qw} { \\qw}; | |
171 | $text .= " $code)"; | |
172 | } | |
74a6a946 JH |
173 | elsif ($Perl5 && $source =~ m/\G\s*(([^\$\@{])[^\$\@{]*)(?=\s*{)/gc |
174 | || $Perl6 && $source =~ m/\G\s*([^:;]*)()/gc) { | |
3ed9f206 JH |
175 | my $code = filter_blocks($1,line(substr($source,0,pos $source),$line)); |
176 | $text .= ' \\' if $2 eq '%'; | |
177 | $text .= " $code)"; | |
178 | } | |
179 | else { | |
74a6a946 | 180 | die "Bad $keyword statement (invalid $keyword value?) near $Switch::file line ", line(substr($source,0,pos $source), $line), "\n"; |
3ed9f206 JH |
181 | } |
182 | ||
74a6a946 JH |
183 | die "Missing colon or semi-colon after 'when' value near $Switch::file line ", line(substr($source,0,pos $source), $line), "\n" |
184 | unless !$Perl6 || $source =~ m/\G(\s*)(:|(?=;))/gc; | |
185 | ||
186 | do{@pos = Text::Balanced::_match_codeblock(\$source,qr/\s*/,qr/\{/,qr/\}/,qr/\{/,qr/\}/,undef)} | |
3ed9f206 JH |
187 | or do { |
188 | if ($source =~ m/\G\s*(?=([};]|\Z))/gc) { | |
189 | $casecounter++; | |
190 | next component; | |
191 | } | |
74a6a946 | 192 | die "Bad $keyword statement (problem in the code block?) near $Switch::file line ", line(substr($source,0,pos $source),$line), "\n"; |
3ed9f206 JH |
193 | }; |
194 | my $code = filter_blocks(substr($source,$pos[0],$pos[4]-$pos[0]),line(substr($source,0,$pos[0]),$line)); | |
195 | $code =~ s/}(?=\s*\Z)/;last S_W_I_T_C_H }/ | |
196 | unless $fallthrough; | |
197 | $text .= "{ while (1) $code continue { goto C_A_S_E_$casecounter } last S_W_I_T_C_H; C_A_S_E_$casecounter: }"; | |
198 | $casecounter++; | |
199 | next component; | |
200 | } | |
201 | ||
d38ca171 | 202 | $source =~ m/\G(\s*(-[sm]\s+|\w+|#.*\n|\W))/gc; |
3ed9f206 JH |
203 | $text .= $1; |
204 | } | |
205 | $text; | |
206 | } | |
207 | ||
208 | ||
209 | ||
210 | sub in | |
211 | { | |
212 | my ($x,$y) = @_; | |
213 | my @numy; | |
214 | for my $nextx ( @$x ) | |
215 | { | |
a1813bef | 216 | my $numx = ref($nextx) || defined $nextx && (~$nextx&$nextx) eq 0; |
3ed9f206 JH |
217 | for my $j ( 0..$#$y ) |
218 | { | |
219 | my $nexty = $y->[$j]; | |
a1813bef | 220 | push @numy, ref($nexty) || defined $nexty && (~$nexty&$nexty) eq 0 |
3ed9f206 JH |
221 | if @numy <= $j; |
222 | return 1 if $numx && $numy[$j] && $nextx==$nexty | |
223 | || $nextx eq $nexty; | |
224 | ||
225 | } | |
226 | } | |
227 | return ""; | |
228 | } | |
229 | ||
230 | sub on_exists | |
231 | { | |
232 | my $ref = @_==1 && ref($_[0]) eq 'HASH' ? $_[0] : { @_ }; | |
233 | [ keys %$ref ] | |
234 | } | |
235 | ||
236 | sub on_defined | |
237 | { | |
238 | my $ref = @_==1 && ref($_[0]) eq 'HASH' ? $_[0] : { @_ }; | |
239 | [ grep { defined $ref->{$_} } keys %$ref ] | |
240 | } | |
241 | ||
242 | sub switch(;$) | |
243 | { | |
244 | my ($s_val) = @_ ? $_[0] : $_; | |
245 | my $s_ref = ref $s_val; | |
246 | ||
247 | if ($s_ref eq 'CODE') | |
248 | { | |
249 | $::_S_W_I_T_C_H = | |
250 | sub { my $c_val = $_[0]; | |
251 | return $s_val == $c_val if ref $c_val eq 'CODE'; | |
252 | return $s_val->(@$c_val) if ref $c_val eq 'ARRAY'; | |
253 | return $s_val->($c_val); | |
254 | }; | |
255 | } | |
a1813bef | 256 | elsif ($s_ref eq "" && defined $s_val && (~$s_val&$s_val) eq 0) # NUMERIC SCALAR |
3ed9f206 JH |
257 | { |
258 | $::_S_W_I_T_C_H = | |
259 | sub { my $c_val = $_[0]; | |
260 | my $c_ref = ref $c_val; | |
261 | return $s_val == $c_val if $c_ref eq "" | |
a1813bef | 262 | && defined $c_val |
3ed9f206 JH |
263 | && (~$c_val&$c_val) eq 0; |
264 | return $s_val eq $c_val if $c_ref eq ""; | |
265 | return in([$s_val],$c_val) if $c_ref eq 'ARRAY'; | |
266 | return $c_val->($s_val) if $c_ref eq 'CODE'; | |
267 | return $c_val->call($s_val) if $c_ref eq 'Switch'; | |
268 | return scalar $s_val=~/$c_val/ | |
269 | if $c_ref eq 'Regexp'; | |
270 | return scalar $c_val->{$s_val} | |
271 | if $c_ref eq 'HASH'; | |
272 | return; | |
273 | }; | |
274 | } | |
275 | elsif ($s_ref eq "") # STRING SCALAR | |
276 | { | |
277 | $::_S_W_I_T_C_H = | |
278 | sub { my $c_val = $_[0]; | |
279 | my $c_ref = ref $c_val; | |
280 | return $s_val eq $c_val if $c_ref eq ""; | |
281 | return in([$s_val],$c_val) if $c_ref eq 'ARRAY'; | |
282 | return $c_val->($s_val) if $c_ref eq 'CODE'; | |
283 | return $c_val->call($s_val) if $c_ref eq 'Switch'; | |
284 | return scalar $s_val=~/$c_val/ | |
285 | if $c_ref eq 'Regexp'; | |
286 | return scalar $c_val->{$s_val} | |
287 | if $c_ref eq 'HASH'; | |
288 | return; | |
289 | }; | |
290 | } | |
291 | elsif ($s_ref eq 'ARRAY') | |
292 | { | |
293 | $::_S_W_I_T_C_H = | |
294 | sub { my $c_val = $_[0]; | |
295 | my $c_ref = ref $c_val; | |
296 | return in($s_val,[$c_val]) if $c_ref eq ""; | |
297 | return in($s_val,$c_val) if $c_ref eq 'ARRAY'; | |
298 | return $c_val->(@$s_val) if $c_ref eq 'CODE'; | |
299 | return $c_val->call(@$s_val) | |
300 | if $c_ref eq 'Switch'; | |
301 | return scalar grep {$_=~/$c_val/} @$s_val | |
302 | if $c_ref eq 'Regexp'; | |
303 | return scalar grep {$c_val->{$_}} @$s_val | |
304 | if $c_ref eq 'HASH'; | |
305 | return; | |
306 | }; | |
307 | } | |
308 | elsif ($s_ref eq 'Regexp') | |
309 | { | |
310 | $::_S_W_I_T_C_H = | |
311 | sub { my $c_val = $_[0]; | |
312 | my $c_ref = ref $c_val; | |
313 | return $c_val=~/s_val/ if $c_ref eq ""; | |
314 | return scalar grep {$_=~/s_val/} @$c_val | |
315 | if $c_ref eq 'ARRAY'; | |
316 | return $c_val->($s_val) if $c_ref eq 'CODE'; | |
317 | return $c_val->call($s_val) if $c_ref eq 'Switch'; | |
318 | return $s_val eq $c_val if $c_ref eq 'Regexp'; | |
319 | return grep {$_=~/$s_val/ && $c_val->{$_}} keys %$c_val | |
320 | if $c_ref eq 'HASH'; | |
321 | return; | |
322 | }; | |
323 | } | |
324 | elsif ($s_ref eq 'HASH') | |
325 | { | |
326 | $::_S_W_I_T_C_H = | |
327 | sub { my $c_val = $_[0]; | |
328 | my $c_ref = ref $c_val; | |
329 | return $s_val->{$c_val} if $c_ref eq ""; | |
330 | return scalar grep {$s_val->{$_}} @$c_val | |
331 | if $c_ref eq 'ARRAY'; | |
332 | return $c_val->($s_val) if $c_ref eq 'CODE'; | |
333 | return $c_val->call($s_val) if $c_ref eq 'Switch'; | |
334 | return grep {$_=~/$c_val/ && $s_val->{"$_"}} keys %$s_val | |
335 | if $c_ref eq 'Regexp'; | |
336 | return $s_val==$c_val if $c_ref eq 'HASH'; | |
337 | return; | |
338 | }; | |
339 | } | |
340 | elsif ($s_ref eq 'Switch') | |
341 | { | |
342 | $::_S_W_I_T_C_H = | |
343 | sub { my $c_val = $_[0]; | |
344 | return $s_val == $c_val if ref $c_val eq 'Switch'; | |
345 | return $s_val->call(@$c_val) | |
346 | if ref $c_val eq 'ARRAY'; | |
347 | return $s_val->call($c_val); | |
348 | }; | |
349 | } | |
350 | else | |
351 | { | |
352 | croak "Cannot switch on $s_ref"; | |
353 | } | |
354 | return 1; | |
355 | } | |
356 | ||
d38ca171 JH |
357 | sub case($) { local $SIG{__WARN__} = \&carp; |
358 | $::_S_W_I_T_C_H->(@_); } | |
3ed9f206 JH |
359 | |
360 | # IMPLEMENT __ | |
361 | ||
362 | my $placeholder = bless { arity=>1, impl=>sub{$_[1+$_[0]]} }; | |
363 | ||
364 | sub __() { $placeholder } | |
365 | ||
366 | sub __arg($) | |
367 | { | |
368 | my $index = $_[0]+1; | |
369 | bless { arity=>0, impl=>sub{$_[$index]} }; | |
370 | } | |
371 | ||
372 | sub hosub(&@) | |
373 | { | |
374 | # WRITE THIS | |
375 | } | |
376 | ||
377 | sub call | |
378 | { | |
379 | my ($self,@args) = @_; | |
380 | return $self->{impl}->(0,@args); | |
381 | } | |
382 | ||
383 | sub meta_bop(&) | |
384 | { | |
385 | my ($op) = @_; | |
386 | sub | |
387 | { | |
388 | my ($left, $right, $reversed) = @_; | |
389 | ($right,$left) = @_ if $reversed; | |
390 | ||
391 | my $rop = ref $right eq 'Switch' | |
392 | ? $right | |
393 | : bless { arity=>0, impl=>sub{$right} }; | |
394 | ||
395 | my $lop = ref $left eq 'Switch' | |
396 | ? $left | |
397 | : bless { arity=>0, impl=>sub{$left} }; | |
398 | ||
399 | my $arity = $lop->{arity} + $rop->{arity}; | |
400 | ||
401 | return bless { | |
402 | arity => $arity, | |
403 | impl => sub { my $start = shift; | |
404 | return $op->($lop->{impl}->($start,@_), | |
405 | $rop->{impl}->($start+$lop->{arity},@_)); | |
406 | } | |
407 | }; | |
408 | }; | |
409 | } | |
410 | ||
411 | sub meta_uop(&) | |
412 | { | |
413 | my ($op) = @_; | |
414 | sub | |
415 | { | |
416 | my ($left) = @_; | |
417 | ||
418 | my $lop = ref $left eq 'Switch' | |
419 | ? $left | |
420 | : bless { arity=>0, impl=>sub{$left} }; | |
421 | ||
422 | my $arity = $lop->{arity}; | |
423 | ||
424 | return bless { | |
425 | arity => $arity, | |
426 | impl => sub { $op->($lop->{impl}->(@_)) } | |
427 | }; | |
428 | }; | |
429 | } | |
430 | ||
431 | ||
432 | use overload | |
433 | "+" => meta_bop {$_[0] + $_[1]}, | |
434 | "-" => meta_bop {$_[0] - $_[1]}, | |
435 | "*" => meta_bop {$_[0] * $_[1]}, | |
436 | "/" => meta_bop {$_[0] / $_[1]}, | |
437 | "%" => meta_bop {$_[0] % $_[1]}, | |
438 | "**" => meta_bop {$_[0] ** $_[1]}, | |
439 | "<<" => meta_bop {$_[0] << $_[1]}, | |
440 | ">>" => meta_bop {$_[0] >> $_[1]}, | |
441 | "x" => meta_bop {$_[0] x $_[1]}, | |
442 | "." => meta_bop {$_[0] . $_[1]}, | |
443 | "<" => meta_bop {$_[0] < $_[1]}, | |
444 | "<=" => meta_bop {$_[0] <= $_[1]}, | |
445 | ">" => meta_bop {$_[0] > $_[1]}, | |
446 | ">=" => meta_bop {$_[0] >= $_[1]}, | |
447 | "==" => meta_bop {$_[0] == $_[1]}, | |
448 | "!=" => meta_bop {$_[0] != $_[1]}, | |
449 | "<=>" => meta_bop {$_[0] <=> $_[1]}, | |
450 | "lt" => meta_bop {$_[0] lt $_[1]}, | |
451 | "le" => meta_bop {$_[0] le $_[1]}, | |
452 | "gt" => meta_bop {$_[0] gt $_[1]}, | |
453 | "ge" => meta_bop {$_[0] ge $_[1]}, | |
454 | "eq" => meta_bop {$_[0] eq $_[1]}, | |
455 | "ne" => meta_bop {$_[0] ne $_[1]}, | |
456 | "cmp" => meta_bop {$_[0] cmp $_[1]}, | |
457 | "\&" => meta_bop {$_[0] & $_[1]}, | |
458 | "^" => meta_bop {$_[0] ^ $_[1]}, | |
459 | "|" => meta_bop {$_[0] | $_[1]}, | |
460 | "atan2" => meta_bop {atan2 $_[0], $_[1]}, | |
461 | ||
462 | "neg" => meta_uop {-$_[0]}, | |
463 | "!" => meta_uop {!$_[0]}, | |
464 | "~" => meta_uop {~$_[0]}, | |
465 | "cos" => meta_uop {cos $_[0]}, | |
466 | "sin" => meta_uop {sin $_[0]}, | |
467 | "exp" => meta_uop {exp $_[0]}, | |
468 | "abs" => meta_uop {abs $_[0]}, | |
469 | "log" => meta_uop {log $_[0]}, | |
470 | "sqrt" => meta_uop {sqrt $_[0]}, | |
471 | "bool" => sub { croak "Can't use && or || in expression containing __" }, | |
472 | ||
473 | # "&()" => sub { $_[0]->{impl} }, | |
474 | ||
475 | # "||" => meta_bop {$_[0] || $_[1]}, | |
476 | # "&&" => meta_bop {$_[0] && $_[1]}, | |
477 | # fallback => 1, | |
478 | ; | |
479 | 1; | |
480 | ||
481 | __END__ | |
482 | ||
483 | ||
484 | =head1 NAME | |
485 | ||
486 | Switch - A switch statement for Perl | |
487 | ||
488 | =head1 VERSION | |
489 | ||
d38ca171 JH |
490 | This document describes version 2.06 of Switch, |
491 | released November 14, 2001. | |
3ed9f206 JH |
492 | |
493 | =head1 SYNOPSIS | |
494 | ||
495 | use Switch; | |
496 | ||
497 | switch ($val) { | |
498 | ||
499 | case 1 { print "number 1" } | |
500 | case "a" { print "string a" } | |
501 | case [1..10,42] { print "number in list" } | |
502 | case (@array) { print "number in list" } | |
503 | case /\w+/ { print "pattern" } | |
504 | case qr/\w+/ { print "pattern" } | |
505 | case (%hash) { print "entry in hash" } | |
506 | case (\%hash) { print "entry in hash" } | |
507 | case (\&sub) { print "arg to subroutine" } | |
508 | else { print "previous case not true" } | |
509 | } | |
510 | ||
511 | =head1 BACKGROUND | |
512 | ||
513 | [Skip ahead to L<"DESCRIPTION"> if you don't care about the whys | |
514 | and wherefores of this control structure] | |
515 | ||
516 | In seeking to devise a "Swiss Army" case mechanism suitable for Perl, | |
517 | it is useful to generalize this notion of distributed conditional | |
518 | testing as far as possible. Specifically, the concept of "matching" | |
519 | between the switch value and the various case values need not be | |
520 | restricted to numeric (or string or referential) equality, as it is in other | |
521 | languages. Indeed, as Table 1 illustrates, Perl | |
522 | offers at least eighteen different ways in which two values could | |
523 | generate a match. | |
524 | ||
525 | Table 1: Matching a switch value ($s) with a case value ($c) | |
526 | ||
527 | Switch Case Type of Match Implied Matching Code | |
528 | Value Value | |
529 | ====== ===== ===================== ============= | |
530 | ||
531 | number same numeric or referential match if $s == $c; | |
532 | or ref equality | |
533 | ||
534 | object method result of method call match if $s->$c(); | |
535 | ref name match if defined $s->$c(); | |
536 | or ref | |
537 | ||
538 | other other string equality match if $s eq $c; | |
539 | non-ref non-ref | |
540 | scalar scalar | |
541 | ||
542 | string regexp pattern match match if $s =~ /$c/; | |
543 | ||
544 | array scalar array entry existence match if 0<=$c && $c<@$s; | |
545 | ref array entry definition match if defined $s->[$c]; | |
546 | array entry truth match if $s->[$c]; | |
547 | ||
548 | array array array intersection match if intersects(@$s, @$c); | |
549 | ref ref (apply this table to | |
550 | all pairs of elements | |
551 | $s->[$i] and | |
552 | $c->[$j]) | |
553 | ||
554 | array regexp array grep match if grep /$c/, @$s; | |
555 | ref | |
556 | ||
557 | hash scalar hash entry existence match if exists $s->{$c}; | |
558 | ref hash entry definition match if defined $s->{$c}; | |
559 | hash entry truth match if $s->{$c}; | |
560 | ||
561 | hash regexp hash grep match if grep /$c/, keys %$s; | |
562 | ref | |
563 | ||
564 | sub scalar return value defn match if defined $s->($c); | |
565 | ref return value truth match if $s->($c); | |
566 | ||
567 | sub array return value defn match if defined $s->(@$c); | |
568 | ref ref return value truth match if $s->(@$c); | |
569 | ||
570 | ||
571 | In reality, Table 1 covers 31 alternatives, because only the equality and | |
572 | intersection tests are commutative; in all other cases, the roles of | |
573 | the C<$s> and C<$c> variables could be reversed to produce a | |
574 | different test. For example, instead of testing a single hash for | |
575 | the existence of a series of keys (C<match if exists $s-E<gt>{$c}>), | |
576 | one could test for the existence of a single key in a series of hashes | |
577 | (C<match if exists $c-E<gt>{$s}>). | |
578 | ||
579 | As L<perltodo> observes, a Perl case mechanism must support all these | |
580 | "ways to do it". | |
581 | ||
582 | ||
583 | =head1 DESCRIPTION | |
584 | ||
585 | The Switch.pm module implements a generalized case mechanism that covers | |
586 | the numerous possible combinations of switch and case values described above. | |
587 | ||
588 | The module augments the standard Perl syntax with two new control | |
589 | statements: C<switch> and C<case>. The C<switch> statement takes a | |
590 | single scalar argument of any type, specified in parentheses. | |
591 | C<switch> stores this value as the | |
592 | current switch value in a (localized) control variable. | |
593 | The value is followed by a block which may contain one or more | |
594 | Perl statements (including the C<case> statement described below). | |
595 | The block is unconditionally executed once the switch value has | |
596 | been cached. | |
597 | ||
598 | A C<case> statement takes a single scalar argument (in mandatory | |
599 | parentheses if it's a variable; otherwise the parens are optional) and | |
600 | selects the appropriate type of matching between that argument and the | |
601 | current switch value. The type of matching used is determined by the | |
602 | respective types of the switch value and the C<case> argument, as | |
603 | specified in Table 1. If the match is successful, the mandatory | |
604 | block associated with the C<case> statement is executed. | |
605 | ||
606 | In most other respects, the C<case> statement is semantically identical | |
607 | to an C<if> statement. For example, it can be followed by an C<else> | |
608 | clause, and can be used as a postfix statement qualifier. | |
609 | ||
610 | However, when a C<case> block has been executed control is automatically | |
611 | transferred to the statement after the immediately enclosing C<switch> | |
612 | block, rather than to the next statement within the block. In other | |
613 | words, the success of any C<case> statement prevents other cases in the | |
614 | same scope from executing. But see L<"Allowing fall-through"> below. | |
615 | ||
616 | Together these two new statements provide a fully generalized case | |
617 | mechanism: | |
618 | ||
619 | use Switch; | |
620 | ||
621 | # AND LATER... | |
622 | ||
623 | %special = ( woohoo => 1, d'oh => 1 ); | |
624 | ||
625 | while (<>) { | |
626 | switch ($_) { | |
627 | ||
74a6a946 JH |
628 | case (%special) { print "homer\n"; } # if $special{$_} |
629 | case /a-z/i { print "alpha\n"; } # if $_ =~ /a-z/i | |
630 | case [1..9] { print "small num\n"; } # if $_ in [1..9] | |
3ed9f206 JH |
631 | |
632 | case { $_[0] >= 10 } { # if $_ >= 10 | |
633 | my $age = <>; | |
634 | switch (sub{ $_[0] < $age } ) { | |
635 | ||
636 | case 20 { print "teens\n"; } # if 20 < $age | |
637 | case 30 { print "twenties\n"; } # if 30 < $age | |
638 | else { print "history\n"; } | |
639 | } | |
640 | } | |
641 | ||
642 | print "must be punctuation\n" case /\W/; # if $_ ~= /\W/ | |
643 | } | |
644 | ||
645 | Note that C<switch>es can be nested within C<case> (or any other) blocks, | |
646 | and a series of C<case> statements can try different types of matches | |
647 | -- hash membership, pattern match, array intersection, simple equality, | |
648 | etc. -- against the same switch value. | |
649 | ||
650 | The use of intersection tests against an array reference is particularly | |
651 | useful for aggregating integral cases: | |
652 | ||
653 | sub classify_digit | |
654 | { | |
655 | switch ($_[0]) { case 0 { return 'zero' } | |
656 | case [2,4,6,8] { return 'even' } | |
657 | case [1,3,4,7,9] { return 'odd' } | |
658 | case /[A-F]/i { return 'hex' } | |
659 | } | |
660 | } | |
661 | ||
662 | ||
663 | =head2 Allowing fall-through | |
664 | ||
665 | Fall-though (trying another case after one has already succeeded) | |
666 | is usually a Bad Idea in a switch statement. However, this | |
667 | is Perl, not a police state, so there I<is> a way to do it, if you must. | |
668 | ||
669 | If a C<case> block executes an untargetted C<next>, control is | |
670 | immediately transferred to the statement I<after> the C<case> statement | |
671 | (i.e. usually another case), rather than out of the surrounding | |
672 | C<switch> block. | |
673 | ||
674 | For example: | |
675 | ||
676 | switch ($val) { | |
677 | case 1 { handle_num_1(); next } # and try next case... | |
678 | case "1" { handle_str_1(); next } # and try next case... | |
679 | case [0..9] { handle_num_any(); } # and we're done | |
680 | case /\d/ { handle_dig_any(); next } # and try next case... | |
681 | case /.*/ { handle_str_any(); next } # and try next case... | |
682 | } | |
683 | ||
684 | If $val held the number C<1>, the above C<switch> block would call the | |
685 | first three C<handle_...> subroutines, jumping to the next case test | |
686 | each time it encountered a C<next>. After the thrid C<case> block | |
687 | was executed, control would jump to the end of the enclosing | |
688 | C<switch> block. | |
689 | ||
690 | On the other hand, if $val held C<10>, then only the last two C<handle_...> | |
691 | subroutines would be called. | |
692 | ||
693 | Note that this mechanism allows the notion of I<conditional fall-through>. | |
694 | For example: | |
695 | ||
696 | switch ($val) { | |
697 | case [0..9] { handle_num_any(); next if $val < 7; } | |
698 | case /\d/ { handle_dig_any(); } | |
699 | } | |
700 | ||
701 | If an untargetted C<last> statement is executed in a case block, this | |
702 | immediately transfers control out of the enclosing C<switch> block | |
703 | (in other words, there is an implicit C<last> at the end of each | |
704 | normal C<case> block). Thus the previous example could also have been | |
705 | written: | |
706 | ||
707 | switch ($val) { | |
708 | case [0..9] { handle_num_any(); last if $val >= 7; next; } | |
709 | case /\d/ { handle_dig_any(); } | |
710 | } | |
711 | ||
712 | ||
713 | =head2 Automating fall-through | |
714 | ||
715 | In situations where case fall-through should be the norm, rather than an | |
716 | exception, an endless succession of terminal C<next>s is tedious and ugly. | |
717 | Hence, it is possible to reverse the default behaviour by specifying | |
718 | the string "fallthrough" when importing the module. For example, the | |
719 | following code is equivalent to the first example in L<"Allowing fall-through">: | |
720 | ||
721 | use Switch 'fallthrough'; | |
722 | ||
723 | switch ($val) { | |
724 | case 1 { handle_num_1(); } | |
725 | case "1" { handle_str_1(); } | |
726 | case [0..9] { handle_num_any(); last } | |
727 | case /\d/ { handle_dig_any(); } | |
728 | case /.*/ { handle_str_any(); } | |
729 | } | |
730 | ||
731 | Note the explicit use of a C<last> to preserve the non-fall-through | |
732 | behaviour of the third case. | |
733 | ||
734 | ||
735 | ||
74a6a946 JH |
736 | =head2 Alternative syntax |
737 | ||
738 | Perl 6 will provide a built-in switch statement with essentially the | |
739 | same semantics as those offered by Switch.pm, but with a different | |
740 | pair of keywords. In Perl 6 C<switch> with be spelled C<given>, and | |
741 | C<case> will be pronounced C<when>. In addition, the C<when> statement | |
742 | will use a colon between its case value and its block (removing the | |
743 | need to parenthesize variables. | |
744 | ||
745 | This future syntax is also available via the Switch.pm module, by | |
746 | importing it with the argument C<"Perl6">. For example: | |
747 | ||
748 | use Switch 'Perl6'; | |
749 | ||
750 | given ($val) { | |
751 | when 1 : { handle_num_1(); } | |
752 | when $str1 : { handle_str_1(); } | |
753 | when [0..9] : { handle_num_any(); last } | |
754 | when /\d/ : { handle_dig_any(); } | |
755 | when /.*/ : { handle_str_any(); } | |
756 | } | |
757 | ||
758 | Note that you can mix and match both syntaxes by importing the module | |
759 | with: | |
760 | ||
761 | use Switch 'Perl5', 'Perl6'; | |
762 | ||
763 | ||
3ed9f206 JH |
764 | =head2 Higher-order Operations |
765 | ||
766 | One situation in which C<switch> and C<case> do not provide a good | |
767 | substitute for a cascaded C<if>, is where a switch value needs to | |
768 | be tested against a series of conditions. For example: | |
769 | ||
770 | sub beverage { | |
771 | switch (shift) { | |
772 | ||
773 | case sub { $_[0] < 10 } { return 'milk' } | |
774 | case sub { $_[0] < 20 } { return 'coke' } | |
775 | case sub { $_[0] < 30 } { return 'beer' } | |
776 | case sub { $_[0] < 40 } { return 'wine' } | |
777 | case sub { $_[0] < 50 } { return 'malt' } | |
778 | case sub { $_[0] < 60 } { return 'Moet' } | |
779 | else { return 'milk' } | |
780 | } | |
781 | } | |
782 | ||
783 | The need to specify each condition as a subroutine block is tiresome. To | |
784 | overcome this, when importing Switch.pm, a special "placeholder" | |
785 | subroutine named C<__> [sic] may also be imported. This subroutine | |
786 | converts (almost) any expression in which it appears to a reference to a | |
787 | higher-order function. That is, the expression: | |
788 | ||
789 | use Switch '__'; | |
790 | ||
791 | __ < 2 + __ | |
792 | ||
793 | is equivalent to: | |
794 | ||
795 | sub { $_[0] < 2 + $_[1] } | |
796 | ||
797 | With C<__>, the previous ugly case statements can be rewritten: | |
798 | ||
799 | case __ < 10 { return 'milk' } | |
800 | case __ < 20 { return 'coke' } | |
801 | case __ < 30 { return 'beer' } | |
802 | case __ < 40 { return 'wine' } | |
803 | case __ < 50 { return 'malt' } | |
804 | case __ < 60 { return 'Moet' } | |
805 | else { return 'milk' } | |
806 | ||
807 | The C<__> subroutine makes extensive use of operator overloading to | |
808 | perform its magic. All operations involving __ are overloaded to | |
809 | produce an anonymous subroutine that implements a lazy version | |
810 | of the original operation. | |
811 | ||
812 | The only problem is that operator overloading does not allow the | |
813 | boolean operators C<&&> and C<||> to be overloaded. So a case statement | |
814 | like this: | |
815 | ||
816 | case 0 <= __ && __ < 10 { return 'digit' } | |
817 | ||
818 | doesn't act as expected, because when it is | |
819 | executed, it constructs two higher order subroutines | |
820 | and then treats the two resulting references as arguments to C<&&>: | |
821 | ||
822 | sub { 0 <= $_[0] } && sub { $_[0] < 10 } | |
823 | ||
824 | This boolean expression is inevitably true, since both references are | |
825 | non-false. Fortunately, the overloaded C<'bool'> operator catches this | |
826 | situation and flags it as a error. | |
827 | ||
828 | =head1 DEPENDENCIES | |
829 | ||
830 | The module is implemented using Filter::Util::Call and Text::Balanced | |
831 | and requires both these modules to be installed. | |
832 | ||
833 | =head1 AUTHOR | |
834 | ||
835 | Damian Conway (damian@conway.org) | |
836 | ||
837 | =head1 BUGS | |
838 | ||
839 | There are undoubtedly serious bugs lurking somewhere in code this funky :-) | |
840 | Bug reports and other feedback are most welcome. | |
841 | ||
d38ca171 JH |
842 | =head1 LIMITATION |
843 | ||
844 | Due to the heuristic nature of Switch.pm's source parsing, the presence | |
845 | of regexes specified with raw C<?...?> delimiters may cause mysterious | |
846 | errors. The workaround is to use C<m?...?> instead. | |
847 | ||
3ed9f206 JH |
848 | =head1 COPYRIGHT |
849 | ||
55a1c97c JH |
850 | Copyright (c) 1997-2001, Damian Conway. All Rights Reserved. |
851 | This module is free software. It may be used, redistributed | |
852 | and/or modified under the same terms as Perl itself. |