[Haskell] -fno-monomorphism-restriction makes type-inference ambiguous?

Eike Scholz eikescholz at gmx.de
Mon Feb 27 10:19:27 EST 2006


thanks for the last help and hints. I have encountered an other problem,
and again I don't quite understand the reason why I get the results I
get. ghci seems to infer different types for the same expression.

Consider that I have disabled the monomorphism restriction 
in module AGC.lhs (which is attached).

and I have a toplevel definition of:

> mylength = synAttr listLength

loding the module in ghci (6.4) gives (beside some correct warnings):

$ Ok, modules loaded: Main.
$ *Main> :type synAttr
$ synAttr :: (Data b) => ((?stack::[Dyn]) => b -> a) -> Attr a

$ *Main> :type listLength
$ listLength :: (?stack::[Dyn]) => List -> Float

$ *Main> :type (synAttr listLength)
$ (synAttr listLength) :: Attr Float

$ *Main> :type mylength
$ mylength :: (?stack::[Dyn]) => Dyn -> Dyn -> [Dyn] -> Maybe Float

$ *Main> let mylength = synAttr listLength
$ *Main> :type mylength
$ mylength :: Dyn -> Dyn -> [Dyn] -> Maybe Float


> type Attr a = Dyn -> Dyn -> [Dyn]-> Maybe a

the problem I have is that inferred types for the toplevel declaration
mylength differ from the verbatim equal definition in the Let

for the toplevel it infers:

  mylength :: (?stack::[Dyn]) => Dyn -> Dyn -> [Dyn] -> Maybe Float

for the let-Binding
  mylength :: Dyn -> Dyn -> [Dyn] -> Maybe Float

and this is what I expected.

Has anyone an Idea, why this happens?

best regards,

  Eike Scholz

PS: Beware of the comments in the attached file. This file is under
heavy development. I am dyslexic and don't correct the comments 
while continuously rewriting code and comments. I hope that the comments
are useful anyway. 
The (+>) (~>) (#>) operators are broken at the moment and don't work the
way intended.

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