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PATH: usr / share / doc / perl-Parse-RecDescent-1.967009 / demo

#!/usr/bin/perl -ws

# THE COMMONEST REASON FOR WANTING LEFT RECURSION

use strict;
use Parse::RecDescent; $::RD_HINT = 1;

my $parse = Parse::RecDescent->new(<<'EndGrammar');

main: expr /\Z/ { $item[1] }
	    | <error>

expr: left_assoc[qw{term add_op term}]
	    | term

add_op: '+'	{ sub { $_[0] + $_[1] } }
	      | '-'	{ sub { $_[0] - $_[1] } }

term: left_assoc[qw{factor mult_op factor}]
	    | factor

mult_op: '*'	{ sub { $_[0] * $_[1] } }
	       | '/'	{ sub { $_[0] / $_[1] } }

factor: number
	      | '(' expr ')' { $item[2] }

number: /[-+]?\d+(\.\d+)?/

# THE BLACK MAGIC THAT MAKES IT WORK...

left_assoc: left_assoc_left[@arg[0,1]](s) <matchrule:$arg[2]>
			{ my @terms = $item[1]
				? ((map { @$_ } @{$item[1]}), $item[2])
				: $item[1];
			  splice @terms, 0, 3, $terms[1]->(@terms[0,2])
				while @terms>1;
			  $terms[0];
			}

left_assoc_left: <matchrule:$arg[0]> <matchrule:$arg[1]>
			{ [ @item[1..2] ] }

EndGrammar

while (<DATA>) {
  print $parse->main($_), "\n";
}

__DATA__
+1-1+1-1+1-1+1-1+1
7*7-6*8
121/(121/11)/121*11
1/(10-1/(1/(10-1)))

[-] demo_cpp.pl [edit]
[-] demo_autorule.pl [edit]
[-] demo_errors.pl [edit]
[-] demo_piecewise.pl [edit]
[-] demo_logic.pl [edit]
[-] demo_skipcomment.pl [edit]
[-] demo_implicit.pl [edit]
[-] demo_separators.pl [edit]
[-] demo_perlparsing.pl [edit]
[-] demo_street.pl [edit]
[-] demo_scoredsep.pl [edit]
[-] demo.c [edit]
[-] demo_textgen.pl [edit]
[-] demo.pl [edit]
[-] demo_calc.pl [edit]
[+] ..
[-] demo_another_Cgrammar.pl [edit]
[-] demo_matchrule2.pl [edit]
[-] demo_mccoy.pl [edit]
[-] demo_restructure_painful.pl [edit]
[-] demo_methods.pl [edit]
[-] demo_language.pl [edit]
[-] demo_selfmod.pl [edit]
[-] demo_OOautoparsetree.pl [edit]
[-] demo_codeblock.pl [edit]
[-] demo_simplequery.pl [edit]
[-] demo_restructure_easy.pl [edit]
[-] demo_tokens.pl [edit]
[-] demo_decomment.pl [edit]
[-] demo_recipe.pl [edit]
[-] demo_delete.pl [edit]
[-] demo_lisplike.pl [edit]
[-] demo_bad.pl [edit]
[-] demo_arithmetic.pl [edit]
[-] demo_leftassoc.pl [edit]
[-] demo_PerlCSV.pl [edit]
[-] demo_metaRD.pm [edit]
[-] demo_derived.pl [edit]
[-] demo_opreps.pl [edit]
[-] demo_matchrule.pl [edit]
[-] demo_LaTeXish_autoact.pl [edit]
[-] demo_operator.pl [edit]
[-] demo_autoscoresep.pl [edit]
[-] demo_Cgrammar_v2.pl [edit]
[-] demo_NL2SQL.pl [edit]
[-] demo_Cgrammar.pl [edit]
[-] demo_randomsentence.pl [edit]
[-] demo_template.pl [edit]
[-] demo_quicklist.pl [edit]
[-] demo_itemhash.pl [edit]
[-] demo_buildcalc.pl [edit]
[-] demo_leftop.pl [edit]
[-] demo_decomment_nonlocal.pl [edit]
[-] demo_dot.pl [edit]
[-] demo_LaTeXish.pl [edit]
[-] demo_precalc.pl [edit]
[-] demo_eval.pl [edit]
[-] demo_autostub.pl [edit]
[-] demo_whoson.pl [edit]
[-] demo_lexer.pl [edit]
[-] demo_OOparsetree.pl [edit]
[-] demo_parsetree.pl [edit]
[-] demo_simple.pl [edit]
[-] demo_embedding.pl [edit]
[-] demo_simpleXML.pl [edit]
[-] demo_undumper.pl [edit]