Could mkWeakPair do what you want?
http://haskell.org/ghc/docs/latest/html/libraries/base/System-Mem-Weak.html#v:mkWeakPair

Or are you trying to do something else?

- Job


2009/11/2 Patai Gergely <patai_gergely@fastmail.fm>
Hello all,

I wanted to create a weak pointer with an IORef as the key and something
else as the value, but I saw no way to do it through the API provided.
After some experimentation I came up with the following abomination for
a solution:

myWeakRef (IORef (STRef r)) v f =
 IO $ \s -> case mkWeak# r v f s of (# s', w #) -> (# s', Weak w #)

This works perfectly when the code is compiled both with and without
optimisations, but ghci chokes on it with an internal error. So my
question is if I can expect this to work at least this much in the long
run, or is it a hopelessly fragile hack?

Gergely

--
http://www.fastmail.fm - Same, same, but different...

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