Is there ever a good reason to use unsafePerformIO?

Question

The question says it all. More specifically, I am writing bindings to a C library, and I\'m wondering what c functions I can use unsafePerformIO with. I assume

Answer 1

Sure. You can have a look at a real example here but in general, unsafePerformIO is usable on any pure function that happens to be side effecting. The IO monad may still be needed to track effects (e.g. freeing memory after the value is computed) even when the function is pure (e.g computing a factorial).

I'm wondering what c functions I can use unsafePerformIO with. I assume using unsafePerformIO with anything involving pointers is a big no-no.

Depends! unsafePerformIO will fully perform actions and force out all the laziness, but that doesn't mean it will break your program. In general, Haskellers prefer unsafePerformIO to appear only in pure functions, so you can use it on results of e.g. scientific computations but maybe not file reads.