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### Re^5: 99 Problems in Perl6

by Ovid (Cardinal)
 on Dec 15, 2006 at 22:44 UTC ( #590141=note: print w/replies, xml ) Need Help??

in reply to Re^4: 99 Problems in Perl6
in thread 99 Problems in Perl6

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

Cheers,
Ovid

New address of my CGI Course.

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Re^6: 99 Problems in Perl6
by gaal (Parson) on Dec 15, 2006 at 22:54 UTC
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.
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;
Didn't we end up using when for guards? The problem with multis for this I seem to remember was that it was hard to spec their order if they're defined in separate compilation units.

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