#14040: Typed holes regression in GHC 8.0.2: No skolem info: z_a1sY[sk:2] -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.10.1 Component: Compiler (Type | Version: 8.0.2 checker) | Keywords: TypeInType, Resolution: | TypeFamilies, | PartialTypeSignatures, TypedHoles Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Compile-time | Test Case: partial- crash or panic | sigs/should_fail/T14040a Blocked By: | Blocking: Related Tickets: #13877, #15076 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): The original program now reports just one error {{{ T14040.hs:41:8: error: • Cannot apply expression of type ‘Sing wl0 -> (forall y. p0 _0 'WeirdNil) -> (forall z1 (x :: z1) (xs :: WeirdList (WeirdList z1)). Sing x -> Sing xs -> p0 _1 xs -> p0 _2 ('WeirdCons x xs)) -> p0 _3 wl0’ to a visible type argument ‘(WeirdList z)’ }}} And that's right: the signature for `elimWierdList` is a partial signature, so we do ''inference'' on the definition. So at the recursive call to `elimWierdList`, the function is a monotype, and can't be applied to type arguments. However, for the `elimWierdList x = error "urk"` version I get {{{ WARNING: file compiler/types/TyCoRep.hs, line 3033 in_scope InScope {a_a10j wl_a10k p_a10l} tenv [aX1 :-> a_a10j[tyv:1], aX2 :-> wl_a10k[tyv:1], aX4 :-> p_a10l[tyv:1]] cenv [] tys [Sing wl_aX2[tyv:1] -> (forall y. p_aX4[tyv:1] __aZo[tau:2] 'WeirdNil) -> (forall z (x :: z) (xs :: WeirdList (WeirdList z)). Sing x -> Sing xs -> p_aX4[tyv:1] __aZL[tau:2] xs -> p_aX4[tyv:1] __aZP[tau:2] ('WeirdCons x xs)) -> p_aX4[tyv:1] __aZW[tau:1] wl_aX2[tyv:1]] cos [] needInScope {z_aX6[sk:2], x_aZm[tau:2], __aZo[tau:2], __aZL[tau:2], __aZP[tau:2], __aZW[tau:1]} Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1211:29 in ghc:Outputable warnPprTrace, called at compiler/types/TyCoRep.hs:3027:6 in ghc:TyCoRep checkValidSubst, called at compiler/types/TyCoRep.hs:3050:29 in ghc:TyCoRep substTy, called at compiler/typecheck/TcSigs.hs:507:49 in ghc:TcSigs ghc-stage1: panic! (the 'impossible' happened) (GHC version 8.7.20190215 for x86_64-unknown-linux): ASSERT failed! 2 0 __a23h[tau:0] Any Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1159:37 in ghc:Outputable pprPanic, called at compiler/utils/Outputable.hs:1220:5 in ghc:Outputable assertPprPanic, called at compiler/typecheck/TcMType.hs:805:54 in ghc:TcMType Please report this as a GHC bug: https://www.haskell.org/ghc/reportabug }}} So there is still stuff wrong here. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14040#comment:19 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler