Fitness-Based Function Testing in Lisp

This code defines a Lisp function called `fitness` that evaluates the fitness of a generated function. It compares the output of the generated function (`form`) with the output of a target function (`fitness-fn`), calculating a fitness value between 0 and 1, where a higher value indicates better fitness. The function includes error handling; it returns `NIL` if the generated function executes illegal code. `fitness` iterates through a list of test inputs (`test-input`), ultimately returning the product of all fitness values as the overall fitness. Examples demonstrate how the function is applied to different generated functions and their fitness scores are calculated.