Functions to test shouldn't be re-evaluated once they were interpreted.

[kmels]

Currently when we call dart-haskell on a file, it will interpret all definitions and save them in the heap. It then tries to test every function but the exploring of which functions to test requires an additional scan through the module.

Solution: Once we interpret an identifier, we should save it's type and when we sail to test, we should look for the types of the already interpreted definitions instead of re-scanning.