Trigger operators

waitTrigger :: Trigger a -> IO a

get next trigger value for this Trigger.

combineTriggers :: [Trigger a] -> IO (Trigger a)

combineTriggers ls merges the triggers in ls into one, such that a value that is signalled on one of the triggers in ls, is signalled on the merged trigger. Useful to implement exclusive choice with.

mapTrigger :: (a->b) -> Trigger a -> Trigger b

mapIOTrigger :: (a-> IO b) -> Trigger a -> Trigger b

mapTrigger f tr creates a new trigger that will signal the transformed value of anything triggered by tr.

filterTrigger :: (a->Bool) -> Trigger a -> Trigger a

filterTrigger pred tr returns a new trigger that will filter the output from tr, letting only through values that satisfy pred.

mapAccumlTrigger ::(a -> b -> (c,b))->b->Trigger a ->IO (Trigger c)

mapAccumlTrigger f v tr returns a new trigger that transforms the output from tr using f and an accumulating parameter (its initial state is v.)

onTriggerDo :: Trigger a -> (a -> IO b) -> Trigger b

onTriggerDo tr action returns a new trigger which returns the value returned by action applied to the output of Trigger tr.

cloneTrigger :: Trigger a -> IO a -> Trigger a

replace the get method for the Trigger with new one, but keep the activate and enable actions of old Trigger intact.

setTriggerName :: String -> Trigger a -> Trigger a

setTriggerName nm tr returns a new trigger that with name nm.

getTriggerName :: Trigger a -> String

returns the trigger name, i.e.,

 nm = getTriggerName (setTriggerName nm tr)

combineTriggers merges a list of triggers into one, and sometimes, we want to be able to change the disabled/enabled state of just a sub-trigger of this super-trigger, i.e., if we represent a menu using a Trigger that has been formed by merging together the items in the menu, it would be really useful if we could selectively changed the interaction state of items via the menu trigger directly.

A trigger can be given a name using setTriggerName, which is used to `guide' the enable/disable operations (see below.) To specify a path through a hierarchy, a list of trigger names, called TriggerNames is used. To illustrate, imagine we have built the following hierarchy using combineTriggers and setTriggerName:

  t1-+---t10
     |
     +---t11
     |
     +---t12
     |
     +---t13
     |
     +---t14

The TriggerName ["t11"] refers to the second trigger of the combined triggers, so doing activateTrigger tr ["t11"] False will disable this item. Similarly, activateTrigger tr ["t1"] False matches Trigger with name t1 and everything underneath it.

isEnabledTrigger :: Trigger a -> TriggerId -> IO Bool

Query the interaction state of a (sub)trigger.

activateTrigger :: Trigger a -> TriggerId -> Bool -> IO ()

Inverse of the above, activateTrigger can be used to selectively turn on and off triggers within a hierarchy:

activateTrigger tr [] False

disables the whole hierarchy.

enableTrigger, disableTrigger :: Trigger a -> IO ()

Convenience functions for activateTrigger tr [] True and activateTrigger tr [] False, respectively.