Very nice! Let's make it work on a hash reference:

$h_ref = { map lc, %$h_ref };

For those of you who don't quite follow, here are the rules:

• In list context, a hash returns a list of key => value pairs. This is the same thing you use when you *create* a hash. There's no guaranteed order, though, which is rather the point.
• map iterates over the elements of a list, applies some transformation to each, and produces an equally-sized list of the results.
• map lc, %list iterates over the keys and values of the hash (by design, a value follows its key) and lowercases each.
• The right side of the expression is evaluated first, so the same variable can be used on both sides.
• Wrapping the map statement in curly braces turns the resulting list into an anonymous hash.</li.
• Assigning that to the original hash reference makes sure the old, potentially upper-cased keys and values are no longer there.

You can get by without the anonymous hash construction, but I thought it was more clear. map is nice.