I wish to add to Christian's question:
why is it not possible to annotate v with its full type:
info :: (Collects e ce, Show e) => ce -> String
info (v::(Collects e ce, Show e) => ce) = show ((one v)::e)
I then get the error message
All of the type variables in the constraint `Collects e
ce' are already in scope
(at least one must be universally quantified here)
In the type: (Collects e ce) => ce
While checking a pattern type signature
When checking the pattern: v :: forall. (Collects e ce) => ce
In the definition of `info':
info (v :: forall. (Collects e ce) => ce) = show ((one v) :: e)
(and a similar message for the constraint Show e),
which I do not understand - why should e and ce be already in scope?
(I think that this question is actually independent of functional
dependencies - it is about type class constraints).
Till
--
Till Mossakowski Phone +49-421-218-4683
Dept. of Computer Science Fax +49-421-218-3054
University of Bremen [EMAIL PROTECTED]
P.O.Box 330440, D-28334 Bremen http://www.tzi.de/~till
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