-- See Note [Newtype coercions] in
-- types/TyCon
Just (arity,coKindFun) | (l,r) <- (coKindFun $ map mkTyVarTy vs) ->
- (vs,l,r) where vs = take arity tyvars
+ -- Here we eta-expand the newtype coercion,
+ -- which makes the ext-core typechecker somewhat simpler.
+ (tyvars,mkAppTys l extraVs,mkAppTys r extraVs)
+ where (vs, extraVs) = (take arity tyvars,
+ map mkTyVarTy $ drop arity tyvars)
Nothing -> pprPanic "MkExternalCore: coercion tcon lacks a kind fun"
(ppr tcon)