#8392: Suggest AllowAmbiguousTypes --------------------------------------------+------------------------------ Reporter: rwbarton | Owner: simonpj Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler (Type checker) | Version: 7.7 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: --------------------------------------------+------------------------------ Changes (by monoidal): * owner: monoidal => simonpj Comment: Simon: I'm passing to you. It's trivial to edit the error message in TcValidity.checkAmbiguity. However, this program {{{ f :: Bool ~ Int => () f = () }}} gives then {{{ Couldn't match type ‛Bool’ with ‛Int’ Inaccessible code in the type signature for f :: Bool ~ Int => () To defer this ambiguity check to use sites, enable AllowAmbiguousTypes In the ambiguity check for: Bool ~ Int => () In the type signature for ‛f’: f :: Bool ~ Int => () }}} and enabling AllowAmbiguousTypes merely changes it to {{{ Couldn't match type ‛Bool’ with ‛Int’ Inaccessible code in the type signature for f :: Bool ~ Int => () }}} So ambiguity check is done before checking inaccessible code, and it might be better to change this order. I don't know if this is simple or has any side effects though. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8392#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler