Perl 6

The syntax is remarkably similar to Ruby, or Ruby is remarkably similar to Perl. Or Perl 6 is remarkably similar to Ruby, which is remarkably similar to Perl 5, 4, 3, 2, 1. Except everything looks like money, the error messages are completely unhelpful, and you can use parens instead of brackets in your function calls.

Fire up the Perl 6 "REPL" and evaluate the code as follows:

EVALFILE 'malc.p6'

Or test directly from the command line:

perl6 malc.p6

You will have to test it using say statements in the original file since this isn't a proper REPL. Supposedly, there is a way to import the code as a module, and you may feel free to submit a pull request to make it so.

How to write a recursive function using anonymous functions in Perl 6

1. Write the function as you normally would without a fixpoint combinator:

my $FACT = -> $n {\
  $IS_ZERO($n)\
    ($ONE)\
    ($MULT($n)($r($PRED($n)))($x))\
  }

2. Wrap the whole thing in FIX, add a parameter (e.g. r) to the front of the definition, and replace all recursive function calls with that parameter:

my $FACT = $FIX(-> $r { -> $n {\
  $IS_ZERO($n)\
    ($ONE)\
    ($MULT($n)($r($PRED($n)))($x))\
  } }\
);

3. Wrap the recursive branch of your function in a dummy closure by adding a parameter (e.g. x) to the front of that branch and applying the last function in that branch to the same parameter:

my $FACT = $FIX(-> $r { -> $n {\
  $IS_ZERO($n)\
    ($ONE)\
    (-> $x { $MULT($n)($r($PRED($n)))($x) })\
  } }\
);

With this method, you can easily convert, e.g. Haskell functions, into Perl 6 anonymous functions that work with malc:

(!!) :: [a] -> Int -> a
(x:_)  !! 0 = x
(_:xs) !! n = xs !! (n-1)

Becomes:

my $INDEX = $FIX(-> $r { -> $xs { -> $n {\
  $IF_THEN_ELSE($IS_ZERO($n))\
    ($HEAD($xs))\
    (-> $x { $r($TAIL($xs))($PRED($n))($x) })\
  } } }\
);

FizzBuzz

Inspired by Tom Stuart, Understanding Computation and Programming with Nothing

my $FIZZBUZZFUNC = $MAP(-> $n {\
  $IF_THEN_ELSE($IS_ZERO($MOD($n)($FIFTEEN)))\
    ($FIZZBUZZ)\
    ($IF_THEN_ELSE($IS_ZERO($MOD($n)($THREE)))\
      ($FIZZ)\
      ($IF_THEN_ELSE($IS_ZERO($MOD($n)($FIVE)))\
        ($BUZZ)\
        ($n)\
    ))\
});

Test the FizzBuzz function by inserting the following line of code into the malc.p6 file:

say $To_FizzBuzz($FIZZBUZZFUNC($RANGE($ONE)($FIFTEEN)));

When you evaluate the file, you should get the following output:

(1 2 Fizz 4 Buzz Fizz 7 8 Fizz Buzz 11 Fizz 13 14 FizzBuzz)