NAME¶

Filter::Template - a source filter for inline code templates (macros)

VERSION¶

version 1.043

SYNOPSIS¶

        use Filter::Template;
        # use Filter::Template ( isa => 'SomeModule' );
        template max (one,two) {
                ((one) > (two) ? (one) : (two))
        }
        print {% max $one, $two %}, "\n";
        const PI 3.14159265359
        print "PI\n";         # Constants are expanded inside strings.
        print "HAPPINESS\n";  # Also expanded due to naive parser.
        enum ZERO ONE TWO
        enum 12 TWELVE THIRTEEN FOURTEEN
        enum + FIFTEEN SIXTEEN SEVENTEEN
        # Prints numbers, due to naive parser.
        print "ZERO ONE TWO TWELVE THIRTEEN FOURTEEN FIFTEEN SIXTEEN SEVENTEEN\n";
        if ($expression) {      # include
                 ... lines of code ...
        }                       # include
        unless ($expression) {  # include
                ... lines of code ...
        } elsif ($expression) { # include
                ... lines of code ...
        } else {                # include
                ... lines of code ...
        }                       # include

DESCRIPTION¶

Filter::Template is a Perl source filter that provides simple inline source code templates. Inlined source code can be significantly faster than subroutines, especially for small-scale functions like accessors and mutators. On the other hand, they are more difficult to maintain and use. Choose your trade-offs wisely.

        template oops {
                die "Oops";
        }

        {% oops %}

        template sum_2 (parameter_0, parameter_1) {
                print( parameter_0 + parameter_1, "\n" );
        }

        {% sum_2 $base, $increment %}

  print( $base + $increment, "\n" );

        const CONSTANT_NAME     'constant value'
        const ANOTHER_CONSTANT  23

        enum ZEROTH FIRST SECOND

        enum 10 TENTH ELEVENTH TWELFTH

        enum 13 THIRTEENTH FOURTEENTH  FIFTEENTH
        enum +  SIXTEENTH  SEVENTEENTH EIGHTEENTH

        if (EXPRESSION) {      # include
                BLOCK;
        } elsif (EXPRESSION) { # include
                BLOCK;
        } else {               # include
                BLOCK;
        }                      # include
        unless (EXPRESSION) {  # include
                BLOCK;
        }                      # include

IMPORTING TEMPLATES¶

Filter::Template can import templates defined by another class. For example, this invocation imports the "use_bytes" template:

        use Filter::Template ( isa => 'Filter::Template::UseBytes' );

Imported templates can be redefined in the current namespace.

Note: If the imported templates require additional Perl modules, any code which imports them must also "use" those modules.

DEBUGGING¶

Filter::Template has three debugging constants which will only take effect if they are defined before the module is first used.

To trace source filtering in general, and to see the resulting code and operations performed on each line, define:

        sub Filter::Template::DEBUG () { 1 }

To trace template invocations as they happen, define:

        sub Filter::Template::DEBUG_INVOKE () { 1 }

To see template, constant, and enum definitions, define:

        sub Filter::Template::DEBUG_DEFINE () { 1 }

To see warnings when a template or constant is redefined, define:

        sub Filter::Template::DEFINE () { 1 }

CAVEATS¶

Source filters are line-based, and so is the template language. The only constructs that may span lines are template definitions, and those must span lines.

Filter::Template does not parse perl. The regular expressions that detect and replace code are simplistic and may not do the right things when parsing challenging Perl syntax. Constants are replaced within strings, for example.

The regexp optimizer makes silly subexpressions like /(?:|m)/. That could be done better as /m?/ or /(?:jklm)?/ if the literal is longer than a single character.

The regexp optimizer does not optimize (?:x|y|z) as character classes.

The regexp optimizer is based on code in Ilya Zakharevich's Text::Trie. Better regexp optimizers were released afterwards, and Filter::Template should use one of them.

LINKS¶

SEE ALSO¶

Text::Trie, PAR, Filter::Template::UseBytes.

AUTHOR & COPYRIGHT¶

Filter::Template is Copyright 2000-2013 Rocco Caputo. Some parts are Copyright 2001 Matt Cashner. All rights reserved. Filter::Template is free software; you may redistribute it and/or modify it under the same terms as Perl itself.

Filter::Template was previously known as POE::Preprocessor.