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-rw-r--r--StackSet.hs8
1 files changed, 4 insertions, 4 deletions
diff --git a/StackSet.hs b/StackSet.hs
index 614e95d..e57e80e 100644
--- a/StackSet.hs
+++ b/StackSet.hs
@@ -303,10 +303,10 @@ differentiate (x:xs) = Just $ Stack x [] xs
-- True. Order is preserved, and focus moves to the next node to the right (if
-- necessary).
filter :: (a -> Bool) -> Stack a -> StackOrNot a
-filter p (Stack f ls rs) = case L.filter p (f:rs) of
- (f':rs') -> Just $ Stack f' (L.filter p ls) rs'
- [] -> do f':rs' <- return $ reverse $ L.filter p ls
- Just $ Stack f' [] rs'
+filter p (Stack f ls rs) = Just $ case L.filter p (f:rs) of
+ (f':rs') -> Stack f' (L.filter p ls) rs'
+ _ -> Stack f' [] rs'
+ where (f':rs') = reverse (L.filter p ls)
-- |
-- /O(s)/. Extract the stack on the current workspace, as a list.