Re: [GHC] #10608: Compile error regression from GHC 7.10 to 7.11

#10608: Compile error regression from GHC 7.10 to 7.11 -------------------------------------+------------------------------------- Reporter: hvr | Owner: simonpj Type: bug | Status: new Priority: normal | Milestone: 7.12.1 Component: Compiler | Version: 7.11 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Other | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by simonpj): Harump. This was deliberate: {{{ commit b83160d07e626bee685f329a9a73e90a4a6074ae Author: Simon Peyton Jones Date: Thu Apr 30 09:18:49 2015 +0100 Tidy up treatment of FlexibleContexts Previously (Trac #10351) we could get Non type-variable argument in the constraint: C [t] (Use FlexibleContexts to permit this) When checking that `f' has the inferred type f :: forall t. C [t] => t -> () which is a bit stupid: we have *inferred* a type that we immediately *reject*. This patch arranges that that the generalisation mechanism (TcSimplify.decideQuantification) doesn't pick a predicate that will be rejected by the subsequent validity check. }}} Moreover #10351 comment 3 makes essentially the same point as you do here. I'll just reverse the change, which is easy to do. Two people have complained about the new behaviour and I don't think anyone complained about the old! Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10608#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler