Control.Eff.Writer.Lazy

Lazy write-only state

Documentation

data Writer w v where

The Writer monad

In MTL's Writer monad, the told value must have a |Monoid| type. Our writer has no such constraints. If we write a |Writer|-like interpreter to accumulate the told values in a monoid, it will have the |Monoid w| constraint then

Constructors

Tell :: w -> Writer w ()

Instances

(MonadBase m m, SetMember (* -> *) (Lift *) (Lift * m) r, MonadBaseControl m (Eff r)) => MonadBaseControl m (Eff ((:) (* -> *) (Writer w) r))

Associated Types

type StM (Eff (((* -> *) ': Writer w) r) :: * -> *) a :: *

Methods

liftBaseWith :: (RunInBase (Eff (((* -> *) ': Writer w) r)) m -> m a) -> Eff (((* -> *) ': Writer w) r) a

restoreM :: StM (Eff (((* -> *) ': Writer w) r)) a -> Eff (((* -> *) ': Writer w) r) a

type StM (Eff ((:) (* -> *) (Writer w) r)) a

type StM (Eff ((:) (* -> *) (Writer w) r)) a = StM (Eff r) (a, [w])

tell :: Member (Writer w) r => w -> Eff r ()

Write a new value.

censor :: forall w a r. Member (Writer w) r => (w -> w) -> Eff r a -> Eff r a

Transform the state being produced.

runWriter :: (w -> b -> b) -> b -> Eff (Writer w ': r) a -> Eff r (a, b)

Handle Writer requests, using a user-provided function to accumulate values, hence no Monoid constraints.

runFirstWriter :: Eff (Writer w ': r) a -> Eff r (a, Maybe w)

Handle Writer requests by taking the first value provided.

runLastWriter :: Eff (Writer w ': r) a -> Eff r (a, Maybe w)

Handle Writer requests by overwriting previous values.

runListWriter :: Eff (Writer w ': r) a -> Eff r (a, [w])

Handle Writer requests, using a List to accumulate values.

runMonoidWriter :: Monoid w => Eff (Writer w ': r) a -> Eff r (a, w)

Handle Writer requests, using a Monoid instance to accumulate values.

execWriter :: (w -> b -> b) -> b -> Eff (Writer w ': r) a -> Eff r b

Handle Writer requests, using a user-provided function to accumulate values and returning the final accumulated values.

execFirstWriter :: Eff (Writer w ': r) a -> Eff r (Maybe w)

Handle Writer requests by taking the first value provided and and returning the final accumulated values.

execLastWriter :: Eff (Writer w ': r) a -> Eff r (Maybe w)

Handle Writer requests by overwriting previous values and returning the final accumulated values.

execListWriter :: Eff (Writer w ': r) a -> Eff r [w]

Handle Writer requests, using a List to accumulate values and returning the final accumulated values.

execMonoidWriter :: Monoid w => Eff (Writer w ': r) a -> Eff r w

Handle Writer requests, using a Monoid instance to accumulate values and returning the final accumulated values.