I'd take a leaf out of Freeforth's compiler (https://github.com/dan4thewin/FreeForth2): It implements a repl via single-pass (as with all forths) compilation of an anonymous block. Scoping in forth is dynamic ie. what's on the stack, and lexical in the dictionary ie. new words can shadow old ones.

Stacks have great GC properties vs. an actual GC, but for more complex scenarios, and dictionary management, some sort of GC would be preferred. I've not looked at the forsp source yet, but it may need a more general (realtime) GC, possibly via a linear-types system.