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I'm passing that 'record' around as an implicit value. The record as STRefs that I use to collect info, but it also has some pure fields with 'read-only' info. Something like,

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data E s = E{ refi :: STRef s Int, refc :: STRef s Char, m :: Int }

In some functions I might need only some pure fields, and none of the STRefs, but since I pass something of type 'E s' around, everything ends up beeing monadic.

there is no reason why that should be the case. you only need to be within the ST monad when you read the references, so if in some function you only look at the pure values, it can have a pure type. hope this helped iavor

That's what I thought, untill I tried it. Well, actually you must be right since the pure field defines a pure (projection) function... Hmmm, ok, can someone explain this to me, data E s = E{ refi :: STRef s Int, refc :: STRef s Char, m :: Int } -- this is fine, obviously... pure :: E s -> Int pure e = m e -- but this is not... pure2 :: (?e :: E s) => Int pure2 = m (?e) Why exactly isn't this allowed? What is the workaround? Error msg: ------------------------------------------------------------------------ Ambiguous constraint `?e :: E s' At least one of the forall'd type variables mentioned by the constraint must be reachable from the type after the '=>' In the type: forall s. (?e :: E s) => Int While checking the type signature for `pure2' Failed, modules loaded: none. -------------------------------------------------------------------------- Thanks, J.A.