I'm no language expert, but the there things I can think of that make bel impractical without major compiler trickery are (1) lack of primitive hash tables (2) lack of primitive arrays (3) no support for tail call optimization (though that third thing is probably fixable with the right compiler tricks)
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.
(1) lack of primitive hash tables (2) lack of primitive arrays
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).
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.