Acme.TimeMachine.Undoable

Documentation

data Suspension s

Data representing the entire history of the state.

data Undoable s a

The undo-able stateful computation monad.

Constructors

Undoable

Fields

getUndoable :: Suspension s -> (Suspension s, a)

Instances

MonadIO TimeMachine

MonadState s (Undoable s)

Monad (Undoable s)

Functor (Undoable s)

Applicative (Undoable s)

evalUndoable :: Undoable s a -> s -> a

Run an undo-able computation and return the result.

>>> evalUndoable (do { return 5 }) 0
5

execUndoable :: Undoable s a -> s -> s

Run an undo-able computation and return the resulting state.

>>> execUndoable (do { modify (+3) }) 0
3

suspend :: Undoable s (Suspension s)

Save the history of a computation, to be later loaded with resume.

resume :: Suspension s -> Undoable s ()

Load the history of a computation, saved by suspend.

undo :: Undoable s ()

Rollback the latest addition to the computation's history.