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Remove unsafe use of head

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This commit is contained in:
Spencer Janssen
2007-05-08 15:21:16 +00:00
parent f03ca10714
commit a846eb18ff
1 changed files with 2 additions and 1 deletions
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3
StackSet.hs
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@@ -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 :: (Integral i, Ord a) => StackSet i j a -> StackSet i j a
promote w = maybe w id $ do promote w = maybe w id $ do
a <- peek w -- fail if null 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 (?) return $ insert a (current w) w' -- and maintain focus (?)
-- | Swap first occurences of 'a' and 'b' in list. -- | Swap first occurences of 'a' and 'b' in list.