summaryrefslogtreecommitdiffstats
diff options
context:
space:
mode:
-rw-r--r--StackSet.hs13
1 files changed, 9 insertions, 4 deletions
diff --git a/StackSet.hs b/StackSet.hs
index e57e80e..f4f482d 100644
--- a/StackSet.hs
+++ b/StackSet.hs
@@ -302,11 +302,16 @@ differentiate (x:xs) = Just $ Stack x [] xs
-- /O(n)/. 'filter p s' returns the elements of 's' such that 'p' evaluates to
-- True. Order is preserved, and focus moves to the next node to the right (if
-- necessary).
+--
+-- Note, this isn't the same as the 'remove' semantics, as focus
+-- won't move 'left' on the end of list.
+--
filter :: (a -> Bool) -> Stack a -> StackOrNot a
-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)
+filter p (Stack f ls rs) = case L.filter p (f:rs) of
+ f':rs' -> Just $ Stack f' (L.filter p ls) rs' -- maybe move focus down
+ [] -> case L.filter p (reverse ls) of -- filter back up
+ f':rs' -> Just $ Stack f' [] rs' -- else up
+ [] -> Nothing
-- |
-- /O(s)/. Extract the stack on the current workspace, as a list.