#12819: Pattern synonym signatures are not validity-checked -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 (Type checker) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: GHC accepts Unknown/Multiple | invalid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Ponder this garbage: {{{#!hs {-# LANGUAGE PatternSynonyms, ViewPatterns, TypeFamilies, KindSignatures #-} module Bug where type family F a -- F :: * -> * data T :: (* -> *) -> * pattern Q :: T F -> String pattern Q x <- (undefined -> x) }}} This is accepted by GHC 8.0.1 and HEAD. But it has an unsaturated type family! Urk! The problem is that `TcSigs.tcPatSynSig` never does validity checking. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12819 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler