hasktags-0.68.7: testcases/monad-base-control.hs

-- to be found MonadBaseControl
-- this tests the utf-8 characters

class MonadBase b m ⇒ MonadBaseControl b m | m → b where
    -- | Monadic state of @m@.
    data StM m ∷ * → *

    -- | @liftBaseWith@ is similar to 'liftIO' and 'liftBase' in that it
    -- lifts a base computation to the constructed monad.
    --
    -- Instances should satisfy similar laws as the 'MonadIO' and 'MonadBase' laws:
    --
    -- @liftBaseWith . const . return = return@
    --
    -- @liftBaseWith (const (m >>= f)) = liftBaseWith (const m) >>= liftBaseWith . const . f@
    --
    -- The difference with 'liftBase' is that before lifting the base computation
    -- @liftBaseWith@ captures the state of @m@. It then provides the base
    -- computation with a 'RunInBase' function that allows running @m@
    -- computations in the base monad on the captured state.
    liftBaseWith ∷ (RunInBase m b → b a) → m a

    -- | Construct a @m@ computation from the monadic state of @m@ that is
    -- returned from a 'RunInBase' function.
    --
    -- Instances should satisfy:
    --
    -- @liftBaseWith (\\runInBase -> runInBase m) >>= restoreM = m@
    restoreM ∷ StM m a → m a

-- | A function that runs a @m@ computation on the monadic state that was
-- captured by 'liftBaseWith'
--
-- A @RunInBase m@ function yields a computation in the base monad of @m@ that
-- returns the monadic state of @m@. This state can later be used to restore the
-- @m@ computation using 'restoreM'.
type RunInBase m b = ∀ a. m a → b (StM m a)