From: Shlomi Fish Date: Fri, 3 Oct 2003 12:34:46 +0000 (+0200) Subject: Re: [PATCH] perlsyn.pod Revision - Resend X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=commitdiff_plain;h=cf48932e9c614884be015feecb615c4d42f6f135;p=p5sagit%2Fp5-mst-13.2.git Re: [PATCH] perlsyn.pod Revision - Resend Message-Id: (Applied with minor tweaks.) p4raw-id: //depot/perl@21405 --- diff --git a/pod/perlsyn.pod b/pod/perlsyn.pod index 257938c..80df487 100644 --- a/pod/perlsyn.pod +++ b/pod/perlsyn.pod @@ -28,16 +28,16 @@ see L for information about how they differ. =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) -until it has been assigned a defined value, which is anything -other than C. When used as a number, C 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 -as a string or a number. Well, usually. Boolean contexts, such as: +The only things you need to declare in Perl are report formats and +subroutines (and sometimes not even subroutines). A variable holds +the undefined value (C) until it has been assigned a defined +value, which is anything other than C. When used as a number, +C is treated as C<0>; when used as a string, it is treated as +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 as a string or a number. Well, usually. Boolean contexts, +such as: my $a; if ($a) {} @@ -94,11 +94,23 @@ expression. The only kind of simple statement is an expression evaluated for its side effects. Every simple statement must be terminated with a semicolon, unless it is the final statement in a block, in which case -the semicolon is optional. (A semicolon is still encouraged there if the -block takes up more than one line, because you may eventually add another line.) -Note that there are some operators like C and C that look -like compound statements, but aren't (they're just TERMs in an expression), -and thus need an explicit termination if used as the last item in a statement. +the semicolon is optional. (A semicolon is still encouraged there if +the block takes up more than one line, because you may eventually add +another line.) Note that there are some operators like C and +C that look like compound statements, but aren't (they're just +TERMs in an expression), and thus need an explicit termination if used +as the last item in a statement. + +=head2 Truth and Falsehood + +A false value is C, the number 0, the string C<'0'> and the +empty string C<''>. Note that unlike some languages, these are three +distinctly different values. A true value is everything which is not +false. + +Note that while 0, 0.0 and C<'0'> are false, C<'0.0'> is true. + +=head2 Statement Modifiers Any simple statement may optionally be followed by a I modifier, just before the terminating semicolon (or block ending). The possible @@ -108,16 +120,36 @@ modifiers are: unless EXPR while EXPR until EXPR - foreach EXPR - -The C and C modifiers have the expected semantics, -presuming you're a speaker of English. The C modifier is an -iterator: For each value in EXPR, it aliases C<$_> to the value and -executes the statement. The C and C modifiers have the -usual "C loop" semantics (conditional evaluated first), except -when applied to a C-BLOCK (or to the deprecated C-SUBROUTINE -statement), in which case the block executes once before the -conditional is evaluated. This is so that you can write loops like: + foreach LIST + +The C following the modifier is referred to as the "condition". +Its truth or falsehood determines how the modifier will behave. + +C executes the statement once I and only if the condition is +true. C is the opposite, it executes the statement I +the condition is true (i.e., if the condition is false). + + print "Basset hounds got long ears" if length $ear >= 10; + go_outside() and play() unless $is_raining; + +The C modifier is an iterator: it executes the statement once +for each item in the LIST (with C<$_> aliased to each item in turn). + + print "Hello $_!\n" foreach qw(world Dolly nurse); + +C repeats the statement I the condition is true. +C does the opposite, it repeats the statement I the +condition is true (or while the condition is false): + + # Both of these count from 0 to 10. + print $i++ while $i <= 10; + print $j++ until $j > 10; + +The C and C modifiers have the usual "C loop" +semantics (conditional evaluated first), except when applied to a +C-BLOCK (or to the deprecated C-SUBROUTINE statement), in +which case the block executes once before the conditional is +evaluated. This is so that you can write loops like: do { $line = ;