#14060: TH-reified types can suffer from kind signature oversaturation -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Template | Version: 8.2.1 Haskell | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I ran into this issue when attempting to fix #11785 in `TcSplice`. Here's a simple Template Haskell program: {{{#!hs {-# LANGUAGE DataKinds #-} {-# LANGUAGE TemplateHaskell #-} module Bug where import Data.Proxy import Language.Haskell.TH newtype Foo = Foo (Proxy '[False, True, False]) $(return []) main :: IO () main = putStrLn $(reify ''Foo >>= stringE . pprint) }}} The output of this program is unfortunately noisy: {{{ $ runghc Bug.hs newtype Bug.Foo = Bug.Foo (Data.Proxy.Proxy ((':) 'GHC.Types.False ((':) 'GHC.Types.True ((':) 'GHC.Types.False ('[] :: [GHC.Types.Bool]) :: [GHC.Types.Bool]) :: [GHC.Types.Bool]) :: [GHC.Types.Bool])) }}} Somehow, we've ended up with four copies of a `[GHC.Types.Bool]` kind annotation! It definitely feels like Template Haskell could be more conservative here in choosing which types get explicit kind annotations - at the most, I'd only expect `'[]` to get one. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14060 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler