state package:adjunctions

Embed a simple state action into the monad.

A generalized State monad, parameterized by a Representable functor. The representation of that functor serves as the state.

A memoized state monad parameterized by a representable functor g, where the representatation of g, Rep g is the state to carry. The return function leaves the state unchanged, while >>= uses the final state of the first computation as the initial state of the second.

A state transformer monad parameterized by:

• g - A representable functor used to memoize results for a state Rep g
• m - The inner monad.

The return function leaves the state unchanged, while >>= uses the final state of the first computation as the initial state of the second.

Minimal definition is either both of get and put or just state

Evaluate a state computation with the given initial state and return the final value, discarding the final state.

• evalState m s = fst (runState m
  s)

Evaluate a state computation with the given initial state and return the final value, discarding the final state.

• evalStateT m s = liftM fst
  (runStateT m s)

Evaluate a state computation with the given initial state and return the final state, discarding the final value.

• execState m s = snd (runState m
  s)

Evaluate a state computation with the given initial state and return the final state, discarding the final value.

• execStateT m s = liftM snd
  (runStateT m s)

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

• runState (mapState f m) = f . runState
  m

Unwrap a state monad computation as a function. (The inverse of state.)