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#!/usr/bin/perl
# https://perlweeklychallenge.org/blog/perl-weekly-challenge-039/
# Task #2
# Write a script to demonstrate Reverse Polish notation(RPN).
# Checkout the wiki page for more information about RPN.
# https://en.wikipedia.org/wiki/Reverse_Polish_notation
use strict;
use warnings;
# the order of the operands is inverted on subroutines
# for the proper operation to take place
# while allowing directly popping from @stack
# without the need of temporary variables
my $operations = {
'+' => sub { $_[1] + $_[0] },
'-' => sub { $_[1] - $_[0] },
# used 'x' instead of '*'
# because I liked the way of adding operands and operators
# as simple command-line argument rather than using a string
'x' => sub { $_[1] * $_[0] },
'/' => sub { $_[1] / $_[0] },
};
my @stack;
while (my $e = shift @ARGV) {
push @stack, $e =~ /^\d+$/ ? $e : $operations->{$e}->(pop @stack,pop @stack)
}
print @stack;
__END__
./ch-2.pl 15 7 1 1 + - / 3 x 2 1 1 + + -
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