#10654: Better error message regarding type synonyms and PolyKinds -------------------------------------+------------------------------------- Reporter: abbradar | Owner: Type: feature | Status: new request | Milestone: Priority: low | Version: 7.10.1 Component: Compiler | Operating System: Unknown/Multiple Keywords: | Type of failure: Other Architecture: | Blocked By: Unknown/Multiple | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Followup of https://mail.haskell.org/pipermail/haskell- cafe/2015-July/120505.html {{{ ghci> :set -XPolyKinds ghci> type Test a = a ghci> type Huh = Test <interactive>:6:1: Type synonym ‘Test’ should have 2 arguments, but has been given 1 In the type declaration for ‘Huh’ }}} (Notice the number of arguments reported) Jonas Scholl at haskell-cafe suggested that the additional invisible argument is a kind argument, which indeed looks to be the case, as he demonstrated: {{{ Prelude> :set -XPolyKinds -XDataKinds -XKindSignatures Prelude> type Test a = a Prelude> type Huh a = Test (a :: Bool) Prelude> type Bar = Huh <interactive>:5:1: Type synonym ‘Huh’ should have 1 argument, but has been given none In the type declaration for ‘Bar’ }}} A better error message may be desirable here. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10654 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler