unsafePerformIO around FFI calls
Tue, 9 Jul 2002 12:04:27 +0100
> Hal Daume <hdaume@ISI.EDU> writes:
> > I'm curious exactly what is "safe" and what is "unsafe" to wrap
> > unsafePerformIO around when it comes to FFI calls.=20
> Here's a simple test:
> Could you imagine an alternative implementation of the same API in
> pure Haskell? (Don't consider efficiency or effort required to write
> the implementation, just whether it can be done.)
> If so, then it is ok to use unsafePerformIO and the ffi to implement
> the API instead.
> If it fails that test, it is incredibly unlikely that it is ok and a
> proof that it is ok is likely to be pretty complex - maybe worth a
> PLDI paper or some such.
That's a nice succinct way to describe it. Another way, which boils
down to the same thing but which is a little more concrete, is to ask:
- Does the function's result depend only on the values of its
(obviously only makes sense for a top-level IO function which you want
to wrap in unsafePerformIO - for a non-top-level function or expression
just replace 'arguments' with 'arguments and free variables').