I think you'd have to hobble Forth pretty badly to make it stand on the same level as Lisp. Lisp has too much hidden machinery- a garbage collector, environment structures, etc. You couldn't even represent forth's "/mod" without resorting to packing results into tuples. Forth is good because every piece of the compiler/interpreter is exposed, usable, and extensible. Lisp wants to keep its innards sealed off and abstracted from the hardware.