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#!/usr/bin/perl -sw
# RPN ARITHMETIC EXPRESSIONS
use Parse::RecDescent;
sub Parse::RecDescent::rpn
{
my @list = @_;
for (my $i=1; $i<@list; $i+=2)
{
@list[$i,$i+1] = @list[$i+1,$i];
}
join " ", @list;
}
# $RD_TRACE=1;
$grammar =
q{
expr : <leftop: conj /(\|\|)/ conj>
{ rpn(@{$item[1]}) }
conj : <leftop: addn /(&&)/ addn>
{ rpn(@{$item[1]}) }
addn : <leftop: mult /([+-])/ mult >
{ rpn(@{$item[1]}) }
mult : <leftop: expo /([*\/\%])/ expo >
{ rpn(@{$item[1]}) }
expo : <leftop: unary /(\^|\*\*)/ unary >
{ rpn(@{$item[1]}) }
unary : '(' expr ')' { $item[2] }
| value
value : /\d+(\.\d+)?/
};
$parse = new Parse::RecDescent ($grammar) or die "bad grammar";
while (<>)
{
print $parse->expr($_), "\n" if $_;
}