#7459: deriving Generic does not work with TypeLits
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Reporter: maxtaldykin | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 7.6.1 | Keywords:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
Failure: GHC rejects valid program | Blockedby:
Blocking: | Related:
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{{{
{-# LANGUAGE DataKinds, KindSignatures #-}
{-# LANGUAGE DeriveGeneric #-}
import GHC.TypeLits
import GHC.Generics
data F (a :: Symbol)
data X = X (F "hello") deriving Generic
}}}
Trying to derive Generics instance for simple datatype with Symbol inside
but GHC complains:
{{{
Can't make a derived instance of `Generic X':
X must not have unlifted or polymorphic arguments
In the data declaration for `X'
}}}
I found that this could be fixed by adding single line to isTauTy:
{{{
--- a/compiler/typecheck/TcType.lhs
+++ b/compiler/typecheck/TcType.lhs
@@ -899,6 +899,7 @@ mkTcEqPred ty1 ty2
isTauTy :: Type -> Bool
isTauTy ty | Just ty' <- tcView ty = isTauTy ty'
isTauTy (TyVarTy _) = True
+isTauTy (LitTy _) = True
isTauTy (TyConApp tc tys) = all isTauTy tys && isTauTyCon tc
isTauTy (AppTy a b) = isTauTy a && isTauTy b
isTauTy (FunTy a b) = isTauTy a && isTauTy b
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7459>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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