Re^2: Fold a list using map splices

[Aristotle]

The index variables there kept tickling me as not right. This is Perl, not C, there has to be a way to do this without explicit indices and no copying. Guess what. :) It's actually simpler than I was expecting and definitely goes in my "cool snippets" file.

sub mapn (&@) {
    my ($cb, $n) = splice @_, 0, 2;
    splice @_, 0, 0, (undef)x$n;
    map{
        splice @_, 0, $n; $cb->(@_[0 .. (@_ < $n ? $#_ : $n-1)]);
    } 0 .. (@_/$n)-1;
}

sub mapnz (&@) {
    my ($cb, $n) = splice @_, 0, 2;
    splice @_, 0, 0, (undef)x$n;
    map{
        splice @_, 0, $n; $cb->(@_[0 .. $n-1]);
    } 0 .. (@_/$n)-1;
}

BrowserUk++ for the inspiration!

Update: fixed mapnz

Makeshifts last the longest.