Hi,
I'm having a problem using Typeable with STRefs. Basically, I want to
store STRefs (among other things) in a universal type. STRef is an
instance of Typeable2, which means that STRef s a is Typeable if s and a
are both Typeable. The problem is that the state type s is opaque and I
can
Having the state be an instance of Typeable breaks the purity
guarantees of runST; a reference could escape runST:
let v = runST (V `liftM` newSTRef 0)
in runST (readSTRef $ fromJust $ getValue v)
Keep in mind that the state actually used by runST is RealWorld;
runST is just a pretty name
Ryan,
So, if I understand you correctly, my only option is to use an IORef
instead of an STRef? What I'm trying to do is implement a mutable box
type as part of a dynamically-typed language I'm implementing in Haskell
(which is mainly an exercise to improve my Haskell programming; mission
On Mon, Mar 16, 2009 at 8:08 PM, Michael Vanier mvanie...@gmail.com wrote:
Ryan,
So, if I understand you correctly, my only option is to use an IORef instead
of an STRef? What I'm trying to do is implement a mutable box type as part
of a dynamically-typed language I'm implementing in Haskell
Why not:
data Value = forall a . Typeable a = V a
type STValue s = STRef Value
This should be:
type STValue s = STRef s Value
Antoine
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