Vgrep.Event

Event handling

An event handler is a function

handleEvent :: MonadState s m => e -> s -> Next (m Redraw)

where e is the event type and s is the state of the handler. The Next type determines the type of action to be performed. The state s is passed as a parameter so the handler can decide which type of action to perform, while not being able to modify the state.

Event handlers form a Monoid where the first handler that triggers will perform the action:

(handleSome <> handleOther) event state

is identical to

case handleSome event state of
    Skip -> handleOther event state
    action -> action

data Next a

The type of action to be performed on an event.

Constructors

Skip

Do not handle the event (fall-through to other event handlers)

Continue a

Handle the event by performing an action

Interrupt Interrupt

Interrupt the application

Instances

Functor Next

Methods

fmap :: (a -> b) -> Next a -> Next b

(<$) :: a -> Next b -> Next a

Monoid (Next a)

The first event handler that triggers (i. e. does not return Skip) handles the event.

Methods

mempty :: Next a

mappend :: Next a -> Next a -> Next a

mconcat :: [Next a] -> Next a

data Redraw

Constructors

Redraw

Indicates that the state has been changed visibly, so the screen should be refreshed.

Unchanged

The state has not changed or the change would not be visible, so refreshing the screen is not required.

Instances

Monoid Redraw

Methods

mempty :: Redraw

mappend :: Redraw -> Redraw -> Redraw

mconcat :: [Redraw] -> Redraw

data Interrupt

Constructors

Suspend (forall m. MonadIO m => Environment -> m ())

Suspend the application and run the action, e. g. invoking an external process, then resume the application.

Halt

Shut down.

Dispatching Events

dispatch :: (e -> Maybe a) -> e -> Next a

If the lookup returns Just action, then handle it with Continue action', otherwise Skip this event handler.

dispatchMap :: Ord e => Map e a -> e -> Next a

Special case of dispatch where actions are looked up from a map.

Re-exports

module Data.Map