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

On second thought, the only reason you have a closure here at all is to preserve state between calls. Use a state variable then, and the more normal function definition syntax. 

sub compress ($x) {
    state $previous;
    if $x ne $previous {
        return $x;
    }
    else {
        return;
    }
}

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Update: I think the if is way too long, but can't remember if there's a context-safe way to return nothing in Perl 6 (that isn't "fail"), to golf out the "return" and say something like return $x ne $previous ?? $x !! $NOTHING_AT_ALL;. In the current application () is probably safe.

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Re^3: 99 Problems in Perl6
by Ovid (Cardinal) on Dec 15, 2006 at 22:29 UTC

    You know, we're getting pretty close to the terseness of Haskell, but (I think) it's still rather readable:

    my $compress = sub ($x) {
    state $previous;
    $x ne $previous ?? $previous = $x !! return;
}

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    And in Haskell:

    compress :: Eq a => [a] -> [a]
compress = map head . group

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    Update: as concise, but less "golfy":

    my $compress = sub ($x) {
    state $previous;
    return $x ne $previous ?? $previous = $x !! ();
}

    [download]

    Cheers,
    Ovid

    New address of my CGI Course.

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[d/l]
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      Here's a version of the Perl 6 code that's almost as terse as average Haskell code:

      my $cmp = sub ($x) {
    state $prv;
    $x ne $prv ?? $prv = $x !! return;
}

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