Btw, I seriously dislike your use of the binary operators for math there. You have much better options to gain speed without obfuscating the code. F.ex, if your @_ check never fails, your indiscriminate use will have cost you much more time than those two binary ops are ever going to save. Futhermore, you're mapping in void context - another waste of effort. (What was he thinking?? -- Ed.) Here is a version that I find more self documenting and more concise - and it even gets rid of one division entirely! :^) 
#!/usr/bin/perl -w
use strict;

sub map2 (&@) {
    my $code = shift;
    if(@_ % 2) {
        require Carp;
        Carp::croak('Odd number of values in list');
    }

    local ($a, $b);
    my @r;

    push @r, $code->() while ($a, $b) = splice @_, 0, 2;
    @r;
}

my %hash = qw/A B C D E F G H/;

# let's remove the multiple calls to print() and
# make the use of a map justifiable, shall we?
print map2 sub { "key $a => value $b\n" }, %hash;

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Update: I can't believe I didn't think about the list being returned. However, the while loop still avoids building a 1 .. @_ / 2 list, thus still saving effort.

Makeshifts last the longest.

In reply to Re: Problem emulating built-ins like map and grep. by Aristotle
in thread Problem emulating built-ins like map and grep. by BrowserUk

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