The joy of writing Perl code with no alphanumerics at all has come up a number times over the years, for example: Re: Fun with one keyword, Re: Fun with one keyword, Acme::EyeDrops.

The other side of the coin is the joy of writing Perl code matching /^[a-z ]+$/ -- which has also been discussed a number of times, for example: Yet Another Obfuscation Engine, exactly 390 bytes.