Provided by: libfilter-template-perl_1.043-3_all 
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.
Templates
Code templates are defined with the "template" statement, which looks a lot like "sub". Because this is
a naive source filter, however, the open brace must be on the same line as the "template" keyword.
Furthermore, the first closing brace in column zero ends a macro body.
template oops {
die "Oops";
}
Templates are inserted into a program using a simple syntax that was adapted from other template
libraries. It was chosen to be compatible with the Perl syntax highlighting of common text editors.
This inserts the body of "template oops".
{% oops %}
Templates can have parameters. The syntax for template parameters was based on prototypes for Perl
subroutines. The two main differences are that parameters are named, and sigils are not used.
template sum_2 (parameter_0, parameter_1) {
print( parameter_0 + parameter_1, "\n" );
}
To insert a template with parameters, simply list the parameters after the template name.
{% sum_2 $base, $increment %}
At expansion time, occurrences of the parameter names within the template are replaced with the source
code provided in the template invocation. In the previous example, "sum_2" literally expands to
print( $base + $increment, "\n" );
and is then compiled by Perl.
Constants and Enumerations
Filter::Template also defines "const" and "enum" keywords. They are essentially simplified templates
without parameters.
"const" defines a constant that is replaced before compile time. Unlike Perl's native constants, these
are not demoted to function calls when Perl is run in debugging or profiling mode.
const CONSTANT_NAME 'constant value'
const ANOTHER_CONSTANT 23
Enumerations are like constants but several sequential integers can be defined in one statement.
Enumerations start from zero by default:
enum ZEROTH FIRST SECOND
If the first parameter of an enumeration is a number, then the enumerated constants will start with that
value:
enum 10 TENTH ELEVENTH TWELFTH
Enumerations may not span lines, but they can be continued. If the first enumeration parameter is the
plus sign, then constants will start where the previous enumeration left off.
enum 13 THIRTEENTH FOURTEENTH FIFTEENTH
enum + SIXTEENTH SEVENTEENTH EIGHTEENTH
Conditional Code Inclusion (#ifdef)
The preprocessor supports something like cpp's #if/#else/#endif by usurping a bit of Perl's conditional
syntax. The following conditional statements will be evaluated at compile time if they are followed by
the comment "# include":
if (EXPRESSION) { # include
BLOCK;
} elsif (EXPRESSION) { # include
BLOCK;
} else { # include
BLOCK;
} # include
unless (EXPRESSION) { # include
BLOCK;
} # include
The code in each conditional statement's BLOCK will be included or excluded in the compiled code
depending on the outcome of its EXPRESSION.
Conditional includes are nestable, but else and elsif must be on the same line as the previous block's
closing brace, as they are in the previous example.
Filter::Template::UseBytes uses conditional code to define different versions of a {% use_bytes %} macro
depending whether the "bytes" pragma exists.
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
BUG TRACKER
https://rt.cpan.org/Dist/Display.html?Status=Active&Queue=Filter-Template
REPOSITORY
http://github.com/rcaputo/filter-template http://gitorious.org/filter-template
OTHER RESOURCES
http://search.cpan.org/dist/Filter-Template/
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.