pod updates (from David Adler, M J T Guy)

[perl5.git] / pod / perlsyn.pod

diff --git a/pod/perlsyn.pod b/pod/perlsyn.pod
index 1f3ae50..f07bdfe 100644 (file)
--- a/pod/perlsyn.pod
+++ b/pod/perlsyn.pod
@@ -5,21 +5,14 @@ perlsyn - Perl syntax
 =head1 DESCRIPTION
 
 A Perl script consists of a sequence of declarations and statements.
 =head1 DESCRIPTION
 
 A Perl script consists of a sequence of declarations and statements.

-The only things that need to be declared in Perl are report formats
-and subroutines.  See the sections below for more information on those
-declarations.  All uninitialized user-created objects are assumed to
-start with a C<null> or C<0> value until they are defined by some explicit
-operation such as assignment.  (Though you can get warnings about the
-use of undefined values if you like.)  The sequence of statements is
-executed just once, unlike in B<sed> and B<awk> scripts, where the
-sequence of statements is executed for each input line.  While this means
-that you must explicitly loop over the lines of your input file (or
-files), it also means you have much more control over which files and
-which lines you look at.  (Actually, I'm lying--it is possible to do an
-implicit loop with either the B<-n> or B<-p> switch.  It's just not the
-mandatory default like it is in B<sed> and B<awk>.)
-
-=head2 Declarations
+The sequence of statements is executed just once, unlike in B<sed>
+and B<awk> scripts, where the sequence of statements is executed
+for each input line.  While this means that you must explicitly
+loop over the lines of your input file (or files), it also means
+you have much more control over which files and which lines you look at.
+(Actually, I'm lying--it is possible to do an implicit loop with
+either the B<-n> or B<-p> switch.  It's just not the mandatory
+default like it is in B<sed> and B<awk>.)

 
 Perl is, for the most part, a free-form language.  (The only exception
 to this is format declarations, for obvious reasons.)  Text from a
 
 Perl is, for the most part, a free-form language.  (The only exception
 to this is format declarations, for obvious reasons.)  Text from a


@@ -29,11 +22,27 @@ interpreted either as division or pattern matching, depending on the
 context, and C++ C<//> comments just look like a null regular
 expression, so don't do that.
 
 context, and C++ C<//> comments just look like a null regular
 expression, so don't do that.
 

+=head2 Declarations
+
+The only things you need to declare in Perl are report formats
+and subroutines--and even undefined subroutines can be handled
+through AUTOLOAD.  A variable holds the undefined value (C<undef>)
+until it has been assigned a defined value, which is anything
+other than C<undef>.  When used as a number, C<undef> is treated
+as C<0>; when used as a string, it is treated the empty string,
+C<"">; and when used as a reference that isn't being assigned
+to, it is treated as an error.  If you enable warnings, you'll
+be notified of an uninitialized value whenever you treat C<undef>
+as a string or a number.  Well, usually.  Boolean ("don't-care")
+contexts and operators such as C<++>, C<-->, C<+=>, C<-=>, and
+C<.=> are always exempt from such warnings.
+

 A declaration can be put anywhere a statement can, but has no effect on
 the execution of the primary sequence of statements--declarations all
 take effect at compile time.  Typically all the declarations are put at
 the beginning or the end of the script.  However, if you're using
 A declaration can be put anywhere a statement can, but has no effect on
 the execution of the primary sequence of statements--declarations all
 take effect at compile time.  Typically all the declarations are put at
 the beginning or the end of the script.  However, if you're using

-lexically-scoped private variables created with C<my()>, you'll have to make sure
+lexically-scoped private variables created with C<my()>, you'll
+have to make sure

 your format or subroutine definition is within the same block scope
 as the my if you expect to be able to access those private variables.
 
 your format or subroutine definition is within the same block scope
 as the my if you expect to be able to access those private variables.