Hi Twan,

Wouter Swierstra wrote:

...

Test.IOSpec Version 1.0

Shouldn't that be 0.1?

You're right of course.

You use Dynamic for the data type in IORefs, this has the unfortunate consequence of needing Typeable constraints. You could try to use unsafeCoerce instead,

...

type Data = () unsafeToData :: a -> Data unsafeToData = unsafeCoerce unsafeFromData :: Data -> a unsafeFromData = unsafeCoerce

I think this should be just as safe as Dynamic, since internally Dynamic uses unsafeCoerce as well. Just steal the details from there.

I'm not entirely happy with the "unsafeFromDynamic" approach I use at the moment. GHC can derive instances of Typeable, so the price you have to pay is not too high. The real problem is that Haskell's type system is not expressive enough to cleanly describe the type of the heap (I know, I could be using HList, but still...). If you're interested, I also have a dependently typed version of the code for IORefs that allows heterogeneous, type-safe, well-scoped pointers. I should probably mention that an ulterior motive for this work is integrating IO in dependently typed languages such as Epigram. It is all, of course, still very much subject to active research. Wouter This message has been checked for viruses but the contents of an attachment may still contain software viruses, which could damage your computer system: you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.