Now I see that, probably, GHC is correct. Thank you. On Jun 30, 2005, Simon Peyton-Jones wrote:
path gets the inferred type path :: forall a. [a]
This polymorphic type is instantiated once when it is passed to 'subterm' and again, quite separately, when it is passed to 'shows'.
| Who knows, please, why does there happen, now and then, the effects | of the following kind? | [..] | The ghc-6-4-branch-June-15-2005 compiler cannot resolve the Show | instances in the following program | (using overlapping and `undecidable' instances): | | ------------------------------------------- | import Dumatel | main = putStr (shows path $ shows (subterm path t) "\n") | where | [..] | t = [..] | | path = [] -- :: SubtermPath | -------------------------------------------