Matthias Görgens wrote:
I have a program that optimizes train schedules. It employs an external solver for Integer Linear Programs. The solve function has the following type:
solve :: Constraints -> IO (Maybe Solution)
And this works. However, my external solver also behaves like a pure function from input to output. I wonder whether this guarantee should be reflected in the type system. I'd also appreciate if the compiler would be able to eliminate some calls to the solver.
solvePure :: Constraints -> Maybe Solution solvePure = unsafePerformIO . solve
Is this a good idea?
This is safe as long as there are no side effects, and not depend on its environment (e.g. don't open files, read from environment variables). In general, functions that do not IO should not have IO in their type signature, because this will contaminate calling functions unnecessarily. Adding 'unsafePerformIO' will work, but a better idea might be to understand why your solver has IO in its type signature. Is this because of FFI calls? You can remove IO in FFI calls if they are free from side effects as well. Regards, -- Jochem Berndsen | jochem@functor.nl GPG: 0xE6FABFAB