GHC doesn't like 'inline' type function applications
{-# LANGUAGE TypeFamilies #-}
import Prelude hiding (foldl, foldr, foldl1, foldr1, mapM_, sequence_,
elem, notElem, concat, concatMap, and, or, any, all,
sum, product, maximum, minimum)
import Data.Monoid
type family Element t
class Foldable t where
foldMap :: Monoid m => (Element t -> m) -> t -> m
foldr :: (Element t -> b -> b) -> b -> t -> b
-- foldr :: Element t ~ a => (a -> b -> b) -> b -> t -> b
foldr f z t = appEndo (foldMap (Endo . f) t) z
GHC chokes on the above module. If the signature of foldr is replaced by the commented one, GHC is happy. It seems to me that the two expressions should be equivalent.
Trac metadata
Trac field | Value |
---|---|
Version | 6.9 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler (Type checker) |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | Unknown |
Architecture | Unknown |