Here I place a Prolog procedure to encode the runlength of a list of symbols. For example: 
[12,2,2,w,3,3,s,s,s,] maps to [1*12,2*2,1*w,2*3,3*s]

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runcode([],C,N,[N*C]).
runcode([H | T],H,N,Z) :- N1 is N+1,runcode(T,H,N1,Z).
runcode([H | T],C,N,[N*C| Z]) :- H\==C,runcode(T,H,1,Z).

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Replies are listed 'Best First'.
Re: PPGA - Prolog-Perl Golf Association: Run-length encoding
by scain (Curate) on Jul 02, 2001 at 19:10 UTC
    Is this like a zen meditation? You know, where the zen master asks you a question that makes no sense so you can free your mind? I don't understand this at all.

    Scott

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Re: PPGA - Prolog-Perl Golf Association: Run-length encoding
by japhy (Canon) on Jul 02, 2001 at 20:32 UTC
    I find a Perl solution a bit more readable: 
    sub runcode {
  my @ret;
  while (@_) {
    my ($x, $c) = (shift, 1);
    $c++, shift while $_[0] eq $x;
    push @ret, "$c*$x";
  }
  return @ret;
}

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    If you want to golf this: 
    # 78 chars
sub RC {
#123456789_123456789_123456789_123456789_123456789_123456789_123456789
+_12345678
 my@r;while(@_){my($x,$c)=(shift,1);$c++,shift while$_[0]eq$x;push@r,"
+$c*$x"}@r
}

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    I'm sure it can be shrunk, but I'm kinda busy right now.

    japhy -- Perl and Regex Hacker
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Re: PPGA - Prolog-Perl Golf Association: Run-length encoding
by clemburg (Curate) on Jul 02, 2001 at 20:30 UTC

    Well, OK.

    (Why do I respond to something like this?)

    This is your Prolog ported to Perl. Now somebody else can make that shorter ;-) ... 

    #!/usr/bin/perl -w
use strict;

my $input = [12, 2, 2, 'w', 3, 3, 's', 's', 's'];
my ($head, @tail) = @{$input};

print "@{runcode(\@tail, $head, 1, [])}";

sub runcode {
    my ($tail, $current_head, $count, $output) = @_;
    return [@{$output}, "$count*$current_head"] 
        unless @{$tail};
    my ($head, @tail) = @{$tail};
    if ("$current_head" eq "$head") {
        return runcode(\@tail, $head, ++$count, $output)
    }
    return runcode(\@tail, 
                   $head, 
                   1, 
                   [@{$output}, "$count*$current_head"]);
}

    [download]

    Christian Lemburg
    Brainbench MVP for Perl
    http://www.brainbench.com

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Re: PPGA - Prolog-Perl Golf Association: Run-length encoding
by chipmunk (Parson) on Jul 02, 2001 at 20:55 UTC
    Here's another golfed Perl solution, at 67 characters: 
    sub rle {
($c)=@_;my$i;map$c ne$_?("$i*$c",$i=1,$c=$_)[0]:++$i&&(),@_,!$_[-1]
}

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[d/l]
      Hmm... this appears signigicantly shorter than the original Prolog. Looks like it's PrincePawn's turn to take a swing at the ball :)

      Just goes to show what a flexible language Perl is.

      TMTOWTSAC!

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Re: PPGA - Prolog-Perl Golf Association: Run-length encoding
by tye (Sage) on Jul 02, 2001 at 22:46 UTC

    I didn't like any of the solutions so far since none of them handle input in the same format as their own output. 

    #!/usr/bin/perl -w
use strict;
sub RunLengthEncode {
    my @out;
    while(  @_  ) {
        my $next= shift;
        if(  ! ref($next)  ) {
            $next= {count=>1,value=>$next};
        }
        if(  @out  &&  $out[$#out]{value} eq $next->{value}  ) {
            $out[$#out]{count} += $next->{count};
        } else {
            push @out, $next;
        }
    }
    return @out;
}
for(  @ARGV  ) {
    print join ",", map { $_->{count}."*".$_->{value} }
        RunLengthEncode( split /,/, $_ );
    print $/;
}

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    But that doesn't define a bunch of rules for "reducing" a problem because, well, it wasn't written in Prolog. (:

            - tye (but my friends call me "Tye")
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Re: PPGA - Prolog-Perl Golf Association: Run-length encoding
by MeowChow (Vicar) on Jul 02, 2001 at 22:06 UTC
    None too pretty, but here's one that gets the job done at 58: 
    sub rle {
  my$c;map{shift;$c++;$_[0]ne$_?do{$a="$_*$c";$c=0;$a}:()}@_
}

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    Though, it has some "issues"... 
       MeowChow                                   
               s aamecha.s a..a\u$&owag.print
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Re: PPGA - Prolog-Perl Golf Association: Run-length encoding (take 2)
by MeowChow (Vicar) on Jul 04, 2001 at 10:55 UTC
    Make that 53 (and strict, to boot) ... ;-) 
    sub rle {
  my$c;map{shift;$c++;$_[0]ne$_?("$_*$c",$c=0)[0]:()}@_
}

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    update: err.. 51 
    sub rle {
  my$c;map{shift;$c++;$_[0]ne$_?"$_*$c"|($c=''):()}@_
}

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       MeowChow                                   
               s aamecha.s a..a\u$&owag.print
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