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Shorter ListZipper solutions #29

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Shorter ListZipper solutions #29

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60 changes: 18 additions & 42 deletions src/Course/ListZipper.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -257,10 +257,9 @@ findLeft ::
(a -> Bool)
-> ListZipper a
-> MaybeListZipper a
findLeft p (ListZipper ls x rs) =
case break p (x:.ls) of
(rs', x':.ls') -> IsZ (ListZipper ls' x' (reverse rs' ++ rs))
_ -> IsNotZ
findLeft p z@(ListZipper _ x _)
| p x = IsZ z
| otherwise = findLeft p -<< moveLeft z

-- | Seek to the right for a location matching a predicate, starting from the
-- current one.
Expand All @@ -275,10 +274,9 @@ findRight ::
(a -> Bool)
-> ListZipper a
-> MaybeListZipper a
findRight p (ListZipper ls x rs) =
case break p (x:.rs) of
(ls', x':.rs') -> IsZ (ListZipper (reverse ls' ++ ls) x' rs')
_ -> IsNotZ
findRight p z@(ListZipper _ x _)
| p x = IsZ z
| otherwise = findRight p -<< moveRight z

-- | Move the zipper left, or if there are no elements to the left, go to the far right.
--
Expand Down Expand Up @@ -322,10 +320,9 @@ moveRightLoop (ListZipper l x (h:.t)) =
moveLeft ::
ListZipper a
-> MaybeListZipper a
moveLeft (ListZipper Nil _ _) =
IsNotZ
moveLeft (ListZipper (h:.t) x r) =
IsZ (ListZipper t h (x:.r))
moveLeft z
| hasLeft z = IsZ (moveLeftLoop z)
| otherwise = IsNotZ

-- | Move the zipper one position to the right.
--
Expand All @@ -337,10 +334,9 @@ moveLeft (ListZipper (h:.t) x r) =
moveRight ::
ListZipper a
-> MaybeListZipper a
moveRight (ListZipper _ _ Nil) =
IsNotZ
moveRight (ListZipper l x (h:.t)) =
IsZ (ListZipper (x:.l) h t)
moveRight z
| hasRight z = IsZ (moveRightLoop z)
| otherwise = IsNotZ

-- | Swap the current focus with the value to the left of focus.
--
Expand Down Expand Up @@ -453,15 +449,10 @@ moveLeftN' ::
Int
-> ListZipper a
-> Either Int (ListZipper a)
moveLeftN' n z =
let moveLeftN'' n' z' q
| n' == 0 = Right z'
| n' < 0 = moveRightN' (negate n') z
| otherwise =
case moveLeft z' of
IsZ zz -> moveLeftN'' (n' - 1) zz (q + 1)
IsNotZ -> Left q
in moveLeftN'' n z 0
moveLeftN' n z@(ListZipper l _ r) =
case moveLeftN n z of
IsZ x -> Right x
IsNotZ -> Left (length (if n > 0 then l else r))

-- | Move the focus right the given number of positions. If the value is negative, move left instead.
-- If the focus cannot be moved, the given number of times, return the value by which it can be moved instead.
Expand All @@ -484,15 +475,7 @@ moveRightN' ::
Int
-> ListZipper a
-> Either Int (ListZipper a)
moveRightN' n z =
let moveRightN'' n' z' q
| n' == 0 = Right z'
| n' < 0 = moveLeftN' (negate n') z
| otherwise =
case moveRight z' of
IsZ zz -> moveRightN'' (n' - 1) zz (q + 1)
IsNotZ -> Left q
in moveRightN'' n z 0
moveRightN' = moveLeftN' . negate

-- | Move the focus to the given absolute position in the zipper. Traverse the zipper only to the extent required.
--
Expand All @@ -508,14 +491,7 @@ nth ::
Int
-> ListZipper a
-> MaybeListZipper a
nth i z =
if i < 0
then
IsNotZ
else
case moveLeftN' i z of
Left a -> moveRightN (i-a) z
Right (ListZipper l _ _) -> moveLeftN (length l) z
nth n z@(ListZipper l _ _) = moveLeftN (length l - n) z

-- | Return the absolute position of the current focus in the zipper.
--
Expand Down