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|
module Accessor
( accessor
, Accessor
, view
, over
, set
, (#)
, (#>)
, listAcc
, fstAcc
, sndAcc
, self
, _0, _1, _2, _3, _4
, _5, _6, _7, _8, _9
)
where
type Accessor s a r = (a -> a) -> s -> (s, r)
accessor :: (s -> a) -> (a -> s -> s) -> Accessor s a a
accessor getter setter f x = (setter newVal x, getter x) where
newVal = f (getter x)
view :: Accessor s a b -> s -> b
view acc = snd . acc id
over :: Accessor s a b -> (a -> a) -> s -> s
over acc f = fst . acc f
set :: Accessor s a b -> a -> s -> s
set acc x = over acc (const x)
infixr #
(#) ::
Accessor obj middle middle -> Accessor middle end end -> Accessor obj end end
(#) = composeAccessors where
composeAccessors ac1 ac2 modifier obj =
(newObj, value)
where
newObj = over ac1 (over ac2 modifier) obj
value = view ac2 (view ac1 obj)
infixr #>
(#>) :: (Functor f) =>
Accessor obj (f middle) (f middle) -> Accessor middle end result
-> Accessor obj end (f result)
(#>) = composeFunctorAccesors where
composeFunctorAccesors ac1 ac2 modifier obj =
(newObj, value)
where
newObj = over ac1 (fmap $ over ac2 modifier) obj
value = fmap (view ac2) (view ac1 obj)
self :: Accessor a a a
self = accessor id const
listAcc :: Int -> Accessor [a] a a
listAcc idx = accessor getter setter where
getter = (!! max 0 idx)
setter n lst = take idx lst ++ [n] ++ drop (idx + 1) lst
_0 :: Accessor [a] a a
_1 :: Accessor [a] a a
_2 :: Accessor [a] a a
_3 :: Accessor [a] a a
_4 :: Accessor [a] a a
_5 :: Accessor [a] a a
_6 :: Accessor [a] a a
_7 :: Accessor [a] a a
_8 :: Accessor [a] a a
_9 :: Accessor [a] a a
_0 = listAcc 0
_1 = listAcc 1
_2 = listAcc 2
_3 = listAcc 3
_4 = listAcc 4
_5 = listAcc 5
_6 = listAcc 6
_7 = listAcc 7
_8 = listAcc 8
_9 = listAcc 9
fstAcc :: Accessor (a, b) a a
fstAcc = accessor getter setter where
getter (a, _) = a
setter n x = (n, snd x)
sndAcc :: Accessor (a, b) b b
sndAcc = accessor getter setter where
getter (_, b) = b
setter n x = (fst x, n)
|
