#15800: Overlapping instances error with single instance -------------------------------------+------------------------------------- Reporter: roland | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by roland): Thanks, this indeed clarifies things! I was trying to trigger the search procedure with `C a Int` as the target constraint. It seems that for the ambiguity check it ended up not only as the target, but also as one of the givens, at which point the error is to be expected. Replacing `()` with `a` (thus making the type non-ambiguous) or adding the AllowAmbiguousTypes pragma both make the program type-check. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15800#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler