Re^4: 99 Problems in Perl6

[gaal]

Your Haskell compress unfortunately bottoms out on empty input. It's otherwise much better than the stateful Perl 6 version.

[Ovid]

Lest anyone think I'm a genius, I stole the Haskell code from here.

[gaal]

The "alternative solution" posted there doesn't suffer from the monomorphism restriction^*, and thus does less to propagate the myth that one has to be a genius to write code in Haskell. It also works correctly with empty input :-)

compress []       = []
compress [a]      = [a]           -- singleton list
compress (x:y:xs) = (if x == y then [] else [x]) ++ compress (y:xs)

^*Something that, for the casual programmer, is quite technical but uninteresting, has a scary name, and a not-that-friendly error message.

[TimToady]

And indeed, you can do that in Perl too:

multi compress () { () }
multi compress ($a) { item $a }
multi compress ($x, $y, *@xs) { $x xx ($x !=== $y), compress($y, |@xs)
+ }

my @x = <a a a a b c c a a d e e e e>;
say perl compress |@x;