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Simplify some functions in ListZipper #22

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Simplify some functions in ListZipper #22

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47 changes: 19 additions & 28 deletions src/Course/ListZipper.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -453,15 +453,11 @@ 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
| n < 0 = moveRightN' (negate n) z
| otherwise = case moveLeftN n z of
IsZ zz -> Right zz
IsNotZ -> Left $ length (lefts z)

-- | 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 +480,11 @@ 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' n z
| n < 0 = moveLeftN' (negate n) z
| otherwise = case moveRightN n z of
IsZ zz -> Right zz
IsNotZ -> Left $ length (rights z)

-- | Move the focus to the given absolute position in the zipper. Traverse the zipper only to the extent required.
--
Expand All @@ -508,14 +500,13 @@ 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
| n < 0 = IsNotZ
| v == 0 = IsZ z
| v < 0 = moveLeftN (negate v) z
| otherwise = moveRightN v z
where
v = n - index z

-- | Return the absolute position of the current focus in the zipper.
--
Expand All @@ -526,8 +517,8 @@ nth i z =
index ::
ListZipper a
-> Int
index (ListZipper l _ _) =
length l
index = length . lefts


-- | Move the focus to the end of the zipper.
--
Expand Down