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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 $_; }