#10019: GHCi cannot reify a custom data constructor with Template Haskell on the first attempt -------------------------------------+------------------------------------- Reporter: | Owner: RyanGlScott | Status: new Type: bug | Milestone: Priority: normal | Version: 7.8.4 Component: Template | Operating System: Unknown/Multiple Haskell | Type of failure: GHC rejects Keywords: | valid program Architecture: | Blocked By: Unknown/Multiple | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- I've uncovered an unusual bug with Template Haskell inside of GHCi. To duplicate it, load GHCi, create a data type, then attempt to reify one of its constructors. It will fail the first time, but succeed the second time. {{{ $ ghci -XTemplateHaskell GHCi, version 7.8.4: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. λ> import Language.Haskell.TH λ> data Option a = Some a | None λ> $(reify 'Some >>= stringE . show) Failed to load interface for ‘Ghci1’ no package matching ‘interactive’ was found λ> $(reify 'Some >>= stringE . show) Loading package array-0.5.0.0 ... linking ... done. Loading package deepseq-1.3.0.2 ... linking ... done. Loading package containers-0.5.5.1 ... linking ... done. Loading package pretty-1.1.1.1 ... linking ... done. Loading package template-haskell ... linking ... done. "DataConI Ghci1.Some (ForallT [PlainTV a_1627392303] [] (AppT (AppT ArrowT (VarT a_1627392303)) (AppT (ConT Ghci1.Option) (VarT a_1627392303)))) Ghci1.Option (Fixity 9 InfixL)" }}} Curiously, this doesn't happen when you reify a data constructor in {{{base}}}, such as {{{Just}}}: {{{ $ ghci -XTemplateHaskell GHCi, version 7.8.4: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. λ> import Language.Haskell.TH λ> $(reify 'Just >>= stringE . show) Loading package array-0.5.0.0 ... linking ... done. Loading package deepseq-1.3.0.2 ... linking ... done. Loading package containers-0.5.5.1 ... linking ... done. Loading package pretty-1.1.1.1 ... linking ... done. Loading package template-haskell ... linking ... done. "DataConI Data.Maybe.Just (ForallT [PlainTV a_1627398816] [] (AppT (AppT ArrowT (VarT a_1627398816)) (AppT (ConT Data.Maybe.Maybe) (VarT a_1627398816)))) Data.Maybe.Maybe (Fixity 9 InfixL)" }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10019 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler