#12393: Poor error message with equational type constraints ---------------------------------+-------------------------------------- Reporter: laneb | Owner: Type: bug | Status: closed Priority: normal | Milestone: Component: GHCi | Version: 8.0.1 Resolution: invalid | Keywords: Operating System: Linux | Architecture: x86_64 (amd64) Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #11469 | Differential Rev(s): Wiki Page: | ---------------------------------+-------------------------------------- Changes (by thomie): * status: new => closed * component: Compiler => GHCi * resolution: => invalid * related: => #11469 Comment: If you turn on `GADTs` or `TypeFamilies` in GHCi, you'll get the error message you were hoping for. {{{ *Test> :set -XGADTs *Test> myFunc "z" <interactive>:3:1: error: • Couldn't match expected type ‘Char’ with actual type ‘FooInner a0’ The type variable ‘a0’ is ambiguous • In the first argument of ‘print’, namely ‘it’ In a stmt of an interactive GHCi command: print it }}} I'm closing this ticket. I agree that the original error message is poor, but #11469 (the ticket referred to in comment:2) will fix the problem. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12393#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler