Category: | Miscellaneous |
Author/Contact Info | Copyright (C) 2001 Brent Dax. All Rights Reserved.
brentdax1@earthlink.net |
Description: | Filter::Interpolate allows you to put something like $(Foo) into a string, and have it interpolate the return value of Foo() in a scalar context. @(Foo) is used for list context. This code is a source filter; it depends on Filter::Simple, which depends on a lot of other things.
Please be gentle; it's very easy to outsmart this module. In particular, $(Foo('(')) will eat your entire program looking for a closing parenthesis (and then die gracefully), while $(Foo(')')) will give you a very strange error message about a missing curly or square bracket. This module can also be used to force context--$() can be used instead of scalar(), and @() can be used instead of the mythical list(). In some cases @() may be the only way to get a list context. I chose these semantics because they're pretty much identical to those proposed for Perl 6. No XS required. POD is embedded. test.pl for this module is available upon request. |
package Filter::Interpolate; use Filter::Simple; FILTER { my($trynext, $parencount, @code)=(0, 0, split //); for(@code) { $trynext=1, next if $_ eq '$'; if($trynext) { if($_ eq '(') { $parencount=1; $_='{\\scalar('; } $trynext=0; } elsif($parencount) { if($_ eq '(') { $parencount++; } elsif($_ eq ')') { $parencount--; $_=')}' unless $parencount; } } } $_=join '', @code; die "Filter::Interpolate: unbalanced parenthesis" if($parencount); ($trynext, $parencount, @code)=(0, 0, split //); for(@code) { $trynext=1, next if $_ eq '@'; if($trynext) { if($_ eq '(') { $parencount=1; $_='{['; } $trynext=0; } elsif($parencount) { if($_ eq '(') { $parencount++; } elsif($_ eq ')') { $parencount--; $_=']}' unless $parencount; } } } die "Filter::Interpolate: unbalanced parenthesis" if($parencount); $_=join '', @code; }; =head1 NAME Filter::Interpolate - Interpolated Function Calls =head1 SYNOPSIS use Filter::Interpolate; sub Foo { '1' } sub Bar { 1..5 } sub Baz { @_ } sub Context { wantarray ? 'list' : 'scalar' } print "Foo: $(Foo)\n"; #prints Foo: 1 print "Bar: @(Bar)\n"; #prints Bar: 1 2 3 4 5 print "Baz: $(Baz('a', 'b'))"; #prints Baz: b print "Baz: @(Baz('a', 'b'))"; #prints Baz: a b print "$(Context)"; #prints scalar print "@(Context)"; #prints list =head1 DESCRIPTION Filter::Interpolate allows you to interpolate function calls into strings. Because of Perl's contexts, Filter::Interpolate requires a sigil (a funny character--$ or @ in this case) to tell the function being called which context to use; thus, the syntax is C<$(>I<call>C<)> for scalar context or C<@(>I<call>C<)> for list context. (This syntax is expected to be used for the same thing in Perl 6, too.) Filter::Interpolate will work on both fuction and method calls. It will work on parenthesized calls c<as long as the parenthesis are balanced>. It even works outside quotes, where it can be used to control context. (This may be the only way to get a list context in some cases, for example.) =head1 BUGS =over 4 =item * Filter::Interpolate doesn't really grok Perl that well, so it can't tell what you mean when you pass a parameter like C<')'>. (It won't have any trouble if you put the other type of parenthesis in front of it, however; the best way to code around this problem is probably something like C<function_call(qw/( )/[1])>.) It can also get confused when a parameter is '(', making it eat your entire program looking for a closing parenthesis. I'm not sure how these problems could be fixed, but I'm looking into it. =item * As strange as it looks, the correct way to interpolate an expression like (Foo)[2] is @(Foo)[2]. This is a side effect of how the module works internally; I'll leave that as-is, since that's (probably) the way Perl 6 will be doing it anyway. =item * This code will look horrible if you try using B::Deparse on it. Y'see, when the module is used, your beautiful $(Foo) is butchered into ${\scalar(Foo)}. Your also-beautiful @(Foo) fares only a little better, becoming @{[Foo]}. (Yes, that's the at-brace-bracket hack.) Just don't try it--you won't be terribly happy with the output's appearance. =back =head1 AUTHOR Copyright (C) 2001 Brent Dax. All rights reserved. This module is free software. It may be used, redistributed and/or modified under the terms of the Perl Artistic License (see http://www.perl.com/perl/misc/Artistic.html). =cut |
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