> dicts certainly involve some thought there

One way to start could be to ignore performance of the data structure.

The first main job dicts are being used for is the `mem` dict mapping a key (variable name) to some value record.

A data structure that supports Store(K, V) & V = Get(K) could be something like an stack allocated array of (Key, Value) pairs, that you search through using linear search to implement Store & Get. It wouldn't be very fast, but you probably don't have too many items in a typical DSL program. You'd need to implement some kind of stack or so on - or perhaps you could get away with reserving some fixed capacity.