Nesting maps isn't difficult, but the idiom for using the $_ of the outer map in the inner map is ugly. A lambda-like idiom with a named $_ would be nicer.

Disclaimer: as can be seen from my previous posts, this is not a criticism of Perl (which is my favorite programming language), but rather ruminations on how to make the code more natural. After writing a lot of code, we all start getting a "feel" for "elegant" code. This is what I'm trying to explore with various programming problems.