Ur型

線形型の文脈内で、非線形の値として扱える

何度でも評価されるかもしれないし、1度も評価されないかもしれない

code:hs

-- | @Ur a@ represents unrestricted values of type @a@ in a linear

-- context. The key idea is that because the contructor holds @a@ with a

-- regular arrow, a function that uses @Ur a@ linearly can use @a@

-- however it likes.

--

-- > someLinear :: Ur a %1-> (a,a)

-- > someLinear (Ur a) = (a,a)

data Ur a where

Ur :: a -> Ur a

簡単な例

code:hs

f' :: a %1 -> (a, a)

f' a = (a, a) -- type error!

code:hs

f :: Ur a %1 -> (a, a)

f (Ur a) = (a, a)

関連

消費

code:hs

consume :: Consumable a => a %1-> ()

複製

code:hs

dup2 :: Dupable a => a %1-> (a,a)

移動

code:hs

move :: Movable a => a %1-> Ur a