#12503: Template Haskell regression: GHC erroneously thinks a type variable is also a kind -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: Type: bug | Status: new Priority: high | Milestone: Component: Template Haskell | Version: 8.0.1 Resolution: | Keywords: TypeInType Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): As before, `Regression2` does in fact compile with GHC 7.10.3: {{{ $ /opt/ghc/7.10.3/bin/ghc Regression2.hs [1 of 1] Compiling Regression2 ( Regression2.hs, Regression2.o ) Regression2.hs:(15,3)-(27,15): Splicing declarations do { FamilyI (FamilyD _ tName_a39r _ _) [DataInstD [] _ [tyVar_a39s] _ _] <- reify ''T; d_a3id <- instanceD (cxt []) (conT ''C `appT` (conT tName_a39r `appT` return tyVar_a39s)) []; return [d_a3id] } ======> instance C (T (b_apE :: k_apP)) }}} There's something interesting to note here, as in GHC 8.0.1, it tries to splice: {{{#!hs instance C (T (b_avD :: b_avO)) }}} But in GHC 7.10.3, it splices this: {{{#!hs instance C (T (b_apE :: k_apP)) }}} Notice that the kind variable isn't `b` at all, but rather an inferred `k`! So it looks like there was a change in behavior at some point. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12503#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler