Sat, 29 Apr 2000 13:22:36 +0200 (MET DST), Tommy Thorn <[EMAIL PROTECTED]> pisze:
> Probable cause: missing `Show a' in type signature for `return'
> Sure there's a missing Show a, but I can't change the signature
> of return and it seems to me that Show a should follow from the
> constraint on TracingEv
Yes, the error message is misleading.
> Is this a fundamental limitation? If so, why?
Where should an error message be reported in the following case?
test:: Monad m => m ()
test = return foldr >> return ()
test':: TracingEnv Int
test' = test >> return 5
Some error must be reported, because the code forces the compiler
to show a function (foldr).
Before we think whether it could be implemented, we must think about
its semantics.
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