mtl-2.2.1: Monad classes, using functional dependencies

Description

Inspired by the paper Functional Programming with Overloading and Higher-Order Polymorphism, Mark P Jones (http://web.cecs.pdx.edu/~mpj/) Advanced School of Functional Programming, 1995.

Synopsis

type RWS r w s = RWST r w s Identity #

A monad containing an environment of type r, output of type w and an updatable state of type s.

rws :: (r -> s -> (a, s, w)) -> RWS r w s a #

Construct an RWS computation from a function. (The inverse of runRWS.)

runRWS :: RWS r w s a -> r -> s -> (a, s, w) #

Unwrap an RWS computation as a function. (The inverse of rws.)

Arguments

 :: RWS r w s a RWS computation to execute -> r initial environment -> s initial value -> (a, w) final value and output

Evaluate a computation with the given initial state and environment, returning the final value and output, discarding the final state.

Arguments

 :: RWS r w s a RWS computation to execute -> r initial environment -> s initial value -> (s, w) final state and output

Evaluate a computation with the given initial state and environment, returning the final state and output, discarding the final value.

mapRWS :: ((a, s, w) -> (b, s, w')) -> RWS r w s a -> RWS r w' s b #

Map the return value, final state and output of a computation using the given function.

• runRWS (mapRWS f m) r s = f (runRWS m r s)

withRWS :: (r' -> s -> (r, s)) -> RWS r w s a -> RWS r' w s a #

withRWS f m executes action m with an initial environment and state modified by applying f.

• runRWS (withRWS f m) r s = uncurry (runRWS m) (f r s)

newtype RWST r w s m a :: * -> * -> * -> (* -> *) -> * -> * #

A monad transformer adding reading an environment of type r, collecting an output of type w and updating a state of type s to an inner monad m.

Constructors

 RWST FieldsrunRWST :: r -> s -> m (a, s, w)

Instances

runRWST :: RWST r w s m a -> r -> s -> m (a, s, w) #

Arguments

 :: Monad m => RWST r w s m a computation to execute -> r initial environment -> s initial value -> m (a, w) computation yielding final value and output

Evaluate a computation with the given initial state and environment, returning the final value and output, discarding the final state.

Arguments

 :: Monad m => RWST r w s m a computation to execute -> r initial environment -> s initial value -> m (s, w) computation yielding final state and output

Evaluate a computation with the given initial state and environment, returning the final state and output, discarding the final value.

mapRWST :: (m (a, s, w) -> n (b, s, w')) -> RWST r w s m a -> RWST r w' s n b #

Map the inner computation using the given function.

• runRWST (mapRWST f m) r s = f (runRWST m r s)

withRWST :: (r' -> s -> (r, s)) -> RWST r w s m a -> RWST r' w s m a #

withRWST f m executes action m with an initial environment and state modified by applying f.

• runRWST (withRWST f m) r s = uncurry (runRWST m) (f r s)