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#!/usr/bin/perl -sw
# A SELF-MODIFYING**2 PARSER
use Parse::RecDescent;
$grammar =
q{
type_defn : 'only' <commit> "$::keyword" is type_name ';'
{ $thisparser->Replace("type_name: '$item[5]'");
print "\"$item[5]\" is now the only valid type name\n";
}
| "$::keyword" <commit> identifier(s) is type_name /('?s)?/ ';'
{ my $newnames = join " | ", map { "'$_'" } @{$item[3]};
$thisparser->Extend("type_name: $newnames");
print "added $newnames as type name(s)\n";
}
| /change\s+$::keyword\s+to/ identifier
{ $::keyword = $item[2];
print "changed $item[0] keyword to: $item[2]\n";
}
| <error>
is : /is|are/
type_name : 'int' | 'float'
identifier: ...!is ...!"$::keyword" ...!type_name /[A-Za-z]\w*/
};
use vars qw { $keyword };
$keyword = "type";
$parse = new Parse::RecDescent ($grammar);
while (<>)
{
$parse->type_defn($_) or print "huh?\n";
}