I've had this same idea before and used this process successfully for fuzzing interpreters, though it was partly manual, partly a hodge podge of shell scripts.

I've had this same idea before and used this process successfully for fuzzing interpreters, though it was partly manual, partly a hodge podge of shell scripts. There are already fuzzers based on this idea, for instance tavor (https://github.com/zimmski/tavor https://github.com/zimmski/tavor). On the purely generative side (no execution), there's blab (https://github.com/aoh/blab https://github.com/aoh/blab). What these lack is probability parameters for each rule so that the probability distribution isn't necessarily uniform.