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#!/usr/bin/perl -sw
# PARSE LOGICAL EXPRESSIONS
use Parse::RecDescent;
$grammar =
q{
expr : '[' <leftop: atom /,?/ atom>(?) ']' { $item[2] }
| '[[' atomlist ']]' { $item[2] }
| disj no_garbage { $item[1] }
| <rightop: atom '=' num>
| <leftop: atom '<<' num>
atomlist: <leftop: atom /,?/ atom>
no_garbage: /^\s*$/
| <error: Trailing garbage: $text>
disj : <leftop: conj /(or)/ conj >
conj : <leftop: unary 'and' unary >
and : 'and'
unary : 'not' atom
| '(' expr ')' { $item[2] }
| atom
atom : /(?!and|or)[a-z]/
num : /\d+/
};
$parse = new Parse::RecDescent ($grammar) or die "bad grammar";
$input = '';
use Data::Dumper;
print "> ";
while (<>)
{
if (/^\.$/) { print STDERR Data::Dumper->Dump([$parse->expr($input)]);
$input = '' }
else { $input .= $_ }
print "> ";
}