Re: [Haskell-cafe] Partially applied type synonyms

bmaxa@Branimirs-Air haskell % ghc -O2 dtchk.hs Loaded package environment from /Users/bmaxa/.ghc/aarch64-darwin-8.10.7/environments/default [1 of 1] Compiling Main ( dtchk.hs, dtchk.o ) Linking dtchk ... bmaxa@Branimirs-Air haskell % ./dtchk dtchk: Prelude.undefined CallStack (from HasCallStack): error, called at libraries/base/GHC/Err.hs:79:14 in base:GHC.Err undefined, called at dtchk.hs:10:5 in main:Main bmaxa@Branimirs-Air haskell % cat dtchk.hs {-# LANGUAGE FlexibleInstances, KindSignatures, LiberalTypeSynonyms, StandaloneDeriving, FlexibleContexts #-} data Foo sx x = Foo sx x deriving (Eq,Show) data Bar (m :: * -> *) = Bar (m Int) deriving instance Show a => Show (Bar (Foo a)) x :: Bar (Foo (Maybe Int)) x = undefined deriving instance Eq a => Eq (Bar (Foo a)) main = print x Greets, Branimir.

On 08.10.2021., at 04:15, Ttt Mmm via Haskell-Cafe wrote:

{-# LANGUAGE FlexibleInstances, KindSignatures, LiberalTypeSynonyms, StandaloneDeriving #-} -- This works: data Foo s x = Foo (s x) x deriving (Eq) -- This replacement doesn't: {- data Foo' sx x = Foo' sx x deriving (Eq) type Foo (s :: * -> *) (x :: *) = Foo' (s x) x -} data Bar (m :: * -> *) = Bar (m Int)

-- Neither of these typecheck: x :: Bar (Foo Maybe) x = undefined deriving instance Eq (Bar (Foo Maybe))