diff options
Diffstat (limited to 'libraries/base/Control/Monad/Fix.hs')
| -rw-r--r-- | libraries/base/Control/Monad/Fix.hs | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/libraries/base/Control/Monad/Fix.hs b/libraries/base/Control/Monad/Fix.hs index c8a9ddab58..568568af84 100644 --- a/libraries/base/Control/Monad/Fix.hs +++ b/libraries/base/Control/Monad/Fix.hs @@ -29,7 +29,7 @@ import Data.Function ( fix ) import Data.Maybe import Data.Monoid ( Dual(..), Sum(..), Product(..) , First(..), Last(..), Alt(..) ) -import GHC.Base ( Monad, errorWithoutStackTrace, (.) ) +import GHC.Base ( Monad, NonEmpty(..), errorWithoutStackTrace, (.) ) import GHC.Generics import GHC.List ( head, tail ) import GHC.ST @@ -74,6 +74,14 @@ instance MonadFix [] where [] -> [] (x:_) -> x : mfix (tail . f) +-- | @since 4.9.0.0 +instance MonadFix NonEmpty where + mfix f = case fix (f . neHead) of + ~(x :| _) -> x :| mfix (neTail . f) + where + neHead ~(a :| _) = a + neTail ~(_ :| as) = as + -- | @since 2.01 instance MonadFix IO where mfix = fixIO |