state package:rebase

Embed a simple state action into the monad.

A state monad parameterized by the type s of 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.

Like modifyTVar' but the function is a simple state transition that can return a side value which is passed on as the result of the STM.

A state transformer monad parameterized by:

• s - The state.
• 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.

Describes the behaviour of a thread when an asynchronous exception is received.

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)

Returns the MaskingState for the current thread.

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

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

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

• runStateT (mapStateT f m) = f .
  runStateT m

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

withState f m executes action m on a state modified by applying f.

• withState f m = modify f >> m

withStateT f m executes action m on a state modified by applying f.

• withStateT f m = modify f >> m