Interesting example of a unit test of sorts for language usability. Got any others?
The other concern I have is the lack of a literal associative data structure syntax (like curly braces in clojure) It seems that would negatively impact pg's goal of "code simplicity" quite a bit.
I'll note that if there are primitive arrays and the compiler optimizes arithmetic, the rest of the hash table can be implemented in Bel.
Also, maybe a Sufficiently Smart Compiler could prove that a list's cdrs will never change, store it in cdr-coded form, and treat it like an array (with the ability to zoom right to, say, element 74087 without chasing a bunch of pointers).