Pipesライブラリ 超図解

pipesライブラリを図解します。

Proxy a' a b' b m r

Pipes.Internalより

data Proxy a' a b' b m r
    = Request a' (a  -> Proxy a' a b' b m r )
    | Respond b  (b' -> Proxy a' a b' b m r )
    | M          (m    (Proxy a' a b' b m r))
    | Pure    r

fb' +>> p

Pipes.Coreより

(+>>)
    :: (Monad m)
    => (b' -> Proxy a' a b' b m r)
    ->        Proxy b' b c' c m r
    ->        Proxy a' a c' c m r
fb' +>> p = case p of
    Request b' fb  -> fb' b' >>~ fb
    Respond c  fc' -> Respond c (\c' -> fb' +>> fc' c')
    M          m   -> M (m >>= \p' -> return (fb' +>> p'))
    Pure       r   -> Pure r

p >>~ fa

Pipes.Coreより

(>>~)
    :: (Monad m)
    =>       Proxy a' a b' b m r
    -> (b -> Proxy b' b c' c m r)
    ->       Proxy a' a c' c m r
p >>~ fb = case p of
    Request a' fa  -> Request a' (\a -> fa a >>~ fb)
    Respond b  fb' -> fb' +>> fb b
    M          m   -> M (m >>= \p' -> return (p' >>~ fb))
    Pure       r   -> Pure r

fb' >\\ p

Pipes.Coreより

(>\\)
    :: (Monad m)
    => (b' -> Proxy a' a y' y m b)
    ->        Proxy b' b y' y m c
    ->        Proxy a' a y' y m c
fb' >\\ p0 = go p0
  where
    go p = case p of
        Request b' fb  -> fb' b' >>= \b -> go (fb b)
        Respond x  fx' -> Respond x (\x' -> go (fx' x'))
        M          m   -> M (m >>= \p' -> return (go p'))
        Pure       a   -> Pure a

p //> fa

Pipes.Coreより

(//>)
    :: (Monad m)
    =>       Proxy x' x b' b m a'
    -> (b -> Proxy x' x c' c m b')
    ->       Proxy x' x c' c m a'
p0 //> fb = go p0
  where
    go p = case p of
        Request x' fx  -> Request x' (\x -> go (fx x))
        Respond b  fb' -> fb b >>= \b' -> go (fb' b')
        M          m   -> M (m >>= \p' -> return (go p'))
        Pure       a   -> Pure a