RPN Take 4

amahabal — 2009-03-03T18:52:07+00:00

fREW++ and pmichaud++ have, between them, three versions of the RPN calculator. Here is a fourth, clener in some ways. You can use it as follows:

> ./perl6 rpn.pl '4 5 9 sqrt + *' 32 > ./perl6 rpn.pl '4 5 9 sqrt rotate3 + *' 35

And here is the code:

my %op_dispatch_table = { '+' => { $^a + $^b }, '-' => { $^a - $^b }, '*' => { $^a * $^b }, '/' => { $^a / $^b }, 'sqrt' => { $^a.sqrt }, 'say' => { $^a.say; $^a}, 'rotate3' => { ($^b, $^c, $^a) }, }; sub evaluate (%odt, $expr) { my @stack; my @tokens = $expr.split(/\s+/); for @tokens { when /^\d+$/ { @stack.push($_); } when ?%odt{$_} { my $f = %odt{$_}; my @top_terms = gather { for 1..$f.arity { take @stack.pop} }; @top_terms = reverse(@top_terms); my @to_push = $f.(|@top_terms); @stack.push(@to_push); } default { die "Unrecognized token '$_'; aborting"; } } @stack.pop; } say "Result: { evaluate(%op_dispatch_table, @*ARGS[0]) }";

I'd like to do even better: when an operator is unrecognized (say "double"), but there is a subroutine of that name in scope we should use that. I will try that next.

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RPN Take 4