rpn3.p6

#!/usr/bin/env perl6

use v6;

# FROM: http://daniel.ruoso.com/categoria/perl/rpn-calculator-perl6 by daniel@ruoso.com

multi infix:<rpn> (@stack, $num where /^ \d+[\.\d+]? $/) {
  [ @stack, $num ];
}
multi infix:<rpn> (@stack, $op where /^ '+' | '-' | '*' | '/' $/) {
  my $lhs = @stack.pop;
  my $rhs = @stack.pop;
  my $res = do given $op {
    when '+' { $rhs + $lhs }
    when '-' { $rhs - $lhs }
    when '*' { $rhs * $lhs }
    when '/' { $rhs / $lhs }
  }
  [ @stack, $res ]
}
multi infix:<rpn> ($any, $unknown) {
  die "Unknown expression near $any $unknown";
}
say [rpn] [], (~@*ARGS).words;