#!//net/perl/5.10.0/bin/perl
use warnings;
use strict;

use 5.010_000;

our @stack;
our $result;

my %operators = (
    '+' => sub { $_[0] += $_[1] },
    '-' => sub { $_[0] -= $_[1] },
    '/' => sub { $_[0] /= $_[1] },
    '*' => sub { $_[0] *= $_[1] },
    '^'  => sub { $_[0]**= $_[1] },
    chs  => sub { $_[0] = -$_[0] },
    abs  => sub { $_[0] = abs $_[0] },
    sqr  => sub { $_[0] *= $_[0] },
    sqrt => sub { $_[0] = sqrt $_[0] },
    sin  => sub { $_[0] = sin $_[0] },
    cos  => sub { $_[0] = cos $_[0] },
    tan  => sub { $_[0] = sin $_[0] / cos $_[0] },
);

my $RPN = qr{
    (?{ @stack = () })
    (?{ $result = undef })
    \A \s*
    (?<start_number> \d+ (?: [.] \d* )? | [.] \d+ )
    (?{ push @stack, $+{start_number} })
    (?>
        \s+
        (?:
            (?<number> \d+ (?: [.] \d* )? | [.] \d+ )
            (?{ push @stack, $+{number} })
        |
            (?<unary_op> chs | abs | sqrt | sqr | sin | cos | tan )
            (?(?{ @stack < 1 }) (*FAIL) )
            (?{ $operators{ $+{unary_op} }->($stack[-1]) })
        |
            (?<binary_op> [-+/*^] )
            (?(?{ @stack < 2 }) (*FAIL) )
            (?{ $operators{ $+{binary_op} }->($stack[-2], pop @stack) })
        )
    )*
    \s* \z
    (?(?{ @stack != 1 }) (*FAIL) )
    (?{ $result = $stack[0] })
}msx,

my %input = (
    'fail'                => undef,
    '1 fail'              => undef,
    '123'                 => 123,
    '123.456'             => 123.456,
    '123.456 +'           => undef,
    '.456'                => .456,
    '123.'                => 123.,
    '123 /'               => undef,
    ' 123 '               => 123,
    '123 chs'             => -123,
    '123 chs chs'         => 123,
    '123 chs chs chs'     => -123,
    '123 chs chs chs chs' => 123,
    '4 2 ^'               => 16,
    '4 2 /'               => 2,
    '4 2 +'               => 6,
    '4 2 *'               => 8,
    '4 2 -'               => 2,
    '12 34+'              => undef,
    '12 34'               => undef,
    '12 34 + +'           => undef,
    '12 34 56 + +'        => 102,
    '12 34 + 56 +'        => 102,
    '123 chs 34 *'        => -4_182,
    '123 34 * chs'        => -4_182,
    '24'                  => 24,
    '24 abs'              => 24,
    '24abs'               => undef,
    '24abssqrt'           => undef,
    '1 24abs+sqrt'        => undef,
    '1 24 abs + sqrt'     => 5,
    '24 chs abs'          => 24,
    '24 chs'              => -24,
    '25 abs sqrt'         => 5,
    '25 chs abs sqrt'     => 5,
    '24 4 + chs sqr'      => 784,
    '34 2 / 2 ^'          => 289,
    '3 34 2 / 2 ^ *'      => 867,
);

foreach my $line ( keys %input ) {
    my ($expression) = $line =~ /($RPN)/;
    if ( !defined $result && !defined $input{$line} ) {
        say "OK: $line is invalid, got no result";
    }
    elsif ( !defined $result ) {
        say "FAILED: $line expected $input{$line}, got no result";
    }
    elsif ( !defined $input{$line} ) {
        say "FAILED: $line got $result, expected no result";
    }
    elsif ( $result == $input{$line} ) {
        say "OK: $expression = $result";
    }
    else {
        say "FAILED: $line got $result, expected $input{$line}";
    }
}