(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).
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).