Some interesting comments on yesterday's Haskell post.  I thought I'd write this in Perl to compare.  Of course, we don't have an "inits" function in the standard library, but that's easily written:

#!/usr/bin/perluse strict; use warnings;use Data::Dumper;

my %hash = (    "key1" =>  1,    "key2" =>  2,    "other" => 3,);

sub inits {    my $string = shift or return;    return ($string, inits( substr($string, 0, -1)) );}

sub getPrefixMap {    my %hash = @_;    return map {        my $k = $_; my $v = $hash{$_};         map { ($_ => $v) } inits $k;    } keys %hash;}

my %map = getPrefixMap( %hash );print Dumper( \%map );

This is a bit noisier, but perhaps more straight-forward than the final haskell version…
Update: broquaint pointed out that the code listing above was missing the zero in the substr, breaking it.  Thanks!