#!/usr/bin/perl
use strict;
use warnings;
use Math::Symbolic;
my $parser = Math::Symbolic::Parser->new();

while (1) {
  print "\n> ";
  my $line = <STDIN>;
  my $tree = $parser->parse($line);
  print("Parse error.\n"), next if not defined $tree;
  print "Entered: $tree\n";
  my $result = $tree->value();
  print("Evaluation error.\n"), next if not defined $result;
  print "Result: $result\n";
}