#14584: Core Lint error -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: | Keywords: TypeInType, | DeferredTypeErrors Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): ...or not. Monoidal's example is amazing. Here's the constraint we get (before simplifying it): {{{ simplifyTop { wanted = WC {wc_impl = Implic { TcLevel = 2 Skolems = k_aGF[sk:2] (m_aGG[sk:2] :: k_aGF[sk:2]) No-eqs = False Status = Unsolved Given = Wanted = WC {wc_simple = [WD] hole{aGP} {0}:: ((m_aGG[sk:2] |> {aGN}) -> (m_aGG[sk:2] |> {aGN}) :: *) GHC.Prim.~# (() :: *) (CNonCanonical) wc_impl = Implic { TcLevel = 3 Skolems = No-eqs = False Status = Unsolved Given = Wanted = WC {wc_simple = [D] _ {0}:: (m_aGG[sk:2] |> {aGN}) -> (m_aGG[sk:2] |> {aGN}) (CHoleCan: TypeHole(_)) [WD] hole{aGN} {0}:: (k_aGF[sk:2] :: *) GHC.Prim.~# (* :: *) (CNonCanonical)} Binds = EvBindsVar<aGO> Needed = [] the inferred type of <expression>_02y :: w_aGJ[tau:3] }} Binds = EvBindsVar<aGQ> Needed = [] the type signature for: f :: forall k (m :: k). () }} }}} Notice that the coercion `{aGN}` is a Wanted inside the inner implication constraint, but is used a constraint (for `{aGP}`) outside that implication. No amount of floating is going to put that right! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14584#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler