Bug in compiling large projects ?

Klaus Lüttich luettich at tzi.de
Wed Aug 25 07:01:41 EDT 2004


I have send a message to these lists a weak ago with almost the same
topic, but I have now additional observations: The problem is not
related to option -O in GHC 6.2.1 ! We use in conjunction these command
line switches for the compilation:
  --make -fglasgow-exts -fallow-overlapping-instances

and get this error message, when we try to compile the complete project:

Compiling Common.Lib.Rel   ( ./Common/Lib/Rel.hs, ./Common/Lib/Rel.o )

    Could not unambiguously deduce (Show (a, a))
	from the context (Show (Rel a), Show a, Ord a)
      arising from use of `show' at ./Common/Lib/Rel.hs:102
    The choice of (overlapping) instance declaration
	depends on the instantiation of `a'
    Probable fix:
	Add (Show (a, a)) to the class or instance method `show'
	Or add an instance declaration for (Show (a, a))
    In the first argument of `(.)', namely `show'
    In the definition of `show':
	show = show . (Common.Lib.Set.fromList . toList)
    In the definition for method `show'

When we issue the same ghc call again, Common/Lib/Rel is compiled
without errors. 
Well, the needed tar-ball (4.2M) to reproduce the error is downloadable

Klaus Lüttich    Email:   luettich at tzi.de
FB 3             Phone:   +49-421-218-7129
Uni Bremen

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