Re: How would I do this in Perl6? #1

[Matt Diephouse]

On Tue, 14 Sep 2004 12:45:17 +0200 (CEST), Michele Dondi
<[EMAIL PROTECTED]> wrote:
> Now I want to take a list of templates, say $t1, ... $tn and get the
> result of
> 
>   $result = pack $tn, ... pack $t2, pack $t1, @input;
> 
> without actually writing the whole thing. To my knowledge and great
> pleasure Perl6 will support currying and a builtin reduce/fold operator.

You could do this with a recursive function (They're your friends. Really.).

    sub extended_pack( [EMAIL PROTECTED] =  ($t1, ... , $tn), [EMAIL PROTECTED] ) {
        # start with the last template so we can use tail recursion
        @input = pack pop(@templates), @input;
        # if there aren't any more templates, we're done
        return @input if not @templates;
        return extended_pack(@templates, [EMAIL PROTECTED]);
    }

Or in Perl 5, which has to use 2 subs to have the same interface (code
untested):

    sub extended_pack {
        my (@input)   = @_;
        my @templates = ($t1, ..., $tn);
        return extended_pack_rec([EMAIL PROTECTED], [EMAIL PROTECTED]);
    }
    
    sub extended_pack_rec {
        my ($input, $templates) = @_;
        @$input = pack pop(@$templates), @$input;
        return @$input if not @$templates;
        # special goto magic for tail recursion
        @_ = ($input, $templates);
        goto &extended_pack_rec;
    }

I prefer Perl 6.

-- 
matt