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# Template Toolkit - parser
This directory contains the YAPP grammar for the Template processor. You
only need to worry about the files in this directory if you want to modify
the template parser grammar. If you're doing such a thing, then it is
assumed that you have some idea of what you're doing.
Parser.yp Yapp grammar file for the Template parser. Skeleton file for ../lib/Template/
yc Simple shell cript to compile grammar and build new
../lib/Template/ file from and
the output rules and states generated from the grammar.
Parser.output Output file generated by the yapp parser. This is
for information and debugging purposes only and can
otherwise be ignored.
README This file
If you don't know what you're doing and would like to, then I can
recommend "Lex and Yacc" by John R. Levine, Tony Mason & Doug Brown
(O'Reilly, ISBN: 1-56592-000-7) which gives a good introduction
to the principles of an LALR parser and how to define grammars in YACC.
YAPP is identical to YACC in all the important ways. See also the
Parse::Yapp documentation and the comments in Template::Parser for more
info. For an in-depth study of parser and compiler theory, consult
"Compiler Theory and Practice", a.k.a. "The Dragon Book", by Alfred
V. Aho, Ravi Sethi and Jeffrey D.Ullman (Addison-Wesley, ISBN:
The parser grammar is compiled by 'yapp', the front-end script to
Francois Desarmenien's Parse::Yapp module(s). You will need Parse::Yapp
version 0.32 or later, available from CPAN, to compile the grammar.
The grammar file that yapp produces (../Template/ contains
the rule and state tables for the grammar. These are then loaded by
Template::Parser and used to run the DFA which is implemented by the
parse_directive() method. This has been derived from the standalone
parser created by Parse::Yapp.
Having modified the Parser.yp file to add your language changes, simply
to compile the grammar and install it in ../lib/Template/
You can then make, make test, make install, or whatever you normally
do, and the new grammar should be used by the template processor. To
revert to the original grammar, simply copy the original distribution
Parser.yp file back into this directory and repeat the above process.
To create a separate grammar, copy and modify the Parser.yp and files as you wish and then run yapp to compile them:
yapp -v -s -o ../lib/Template/ \
-t MyParser.yp
You can then instantiate you own grammar and pass this to the
Template constructor.
my $template = Template->new({
GRAMMAR => Template::MyGrammar->new(),
Changing the grammar is a simple process, in theory at least, if you're
familiar with YAPP/YACC. In practice, it also requires some insight
into the inner working of the template toolkit which should probably
be better documented somewhere.
Andy Wardley <>
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