diff options
| -rw-r--r-- | StackSet.hs | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/StackSet.hs b/StackSet.hs index 38baca2..e0210f1 100644 --- a/StackSet.hs +++ b/StackSet.hs @@ -188,7 +188,8 @@ raiseFocus k w = case M.lookup k (cache w) of promote :: (Integral i, Ord a) => StackSet i j a -> StackSet i j a promote w = maybe w id $ do a <- peek w -- fail if null - let w' = w { stacks = M.adjust (\(f, s) -> (f, swap a (head s) s)) (current w) (stacks w) } + (f, xs@(x:_)) <- M.lookup (current w) (stacks w) + let w' = w { stacks = M.insert (current w) (f, swap a x xs) (stacks w) } return $ insert a (current w) w' -- and maintain focus (?) -- | Swap first occurences of 'a' and 'b' in list. |