Unfortunately it didn't work.
The error message is not so clear to me and my understanding in advanced
Haskell type system is yet to weak to figure out what is going on.
Looking at the error messages seems that the type inference analyzes the
code in two different direction and finds some inconsistency at some
junction point.
Couldn't match type `Unit subUnit3' with `Unit subUnit2'
NB: `Unit' is a type function, and may not be injective
How can I say that "Unit subUnit3" is "Unit subUnit2"?
The type of error message seems be caused by a very similar problem
Could not deduce (a1 ~ ActiveSubUnit subUnit3)
.......
Expected type: SetActiveSubUnits a
Actual type: Set (ActiveSubUnit subUnit3)
since "SetActiveSubUnits a" and "Set (ActiveSubUnit subUnit3)" should have
the same type.
Any new idea ?
Cheers,
Edgar Gomes
On 26 March 2011 16:13, Stephen Tetley
For the specific error at line 265 I think you should be using ScopedTypeVariables and properly qualifying the type signature at the function level with a forall.
The local annotation { ::(SubUnit a)=> } is presumably introducing another type variable unrelated to 'a' in the function level type signature.
Note, my suggestion is "by eye" - I haven't run the code, so it may not work or there may be other errors.
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