CODEWITHSUNDEEP
eclipsegrammarmodelingxtextxpand
weltraumpirat
weltraumpirat

Reputation: 22604

Make either a reference or a terminal accessible through the same element name in Xtext/Xpand?

I have an Xtext grammar that describes statemachines, and I have been using references to previously declared events and states to describe transitions:

Event:
 'event' name=ID
 ;

State:
 'state' name=ID
 ;

Transition:
 event=[Event] '=>' state=[State]
    ;

When I use MWE to generate an editor, it will validate the existence of referenced items. For example, writing 

init => idle

would require these: 

event init
state idle

to be present somewhere else in the code (btw I am using one file for each statemachine, so it needs to be in the same file). In my Xpand code templates, I can access event and state as elements of transition:

«FOREACH statemachine.transitions.event AS event-» // you get the idea

This works really well, and I have been using it for quite a while.

But since a number of events are common to all of my statemachines (init, show, hide, finish, and a few more), I want to be able to either reference an event the way I used to, or enter one of the above event names without having to declare the event in every file.

But I can't do this:

Transition:
 event=( [Event] | ('init'|'show'|'hide'|'finish') ) '=>' state=[State]
    ;

So I decided to define a terminal EventID, which is either of said keywords:

terminal EventID:
     'init'|'show'|'hide'|'finish'
     ;

But I also can't do this:

Transition:
 event=( [Event] | EventID ) '=>' state=[State]
    ;

Then I tried making Event a combined rule:

CustomEvent:
    'event' name=ID
    ;

BaseEvent:
    name=EventID
    ;

Event:
    CustomEvent | BaseEvent
    ;

Transition:
    event=[Event] '=>' state=[State]
    ;

which didn't work either.

For now I have decided to settle for a workaround:

Transition:
    ( event=[Event] | baseevent=EventID ) '=>' state=[State]
    ;

This works, but I will have to change all my templates to look for both events and baseevents.

I realize, this is quite a lot of text... So finally, here's my question:

Is there any way at all I can use the same element name for either a reference or an EventID?

Upvotes: 3

Views: 170

Answers (1)

fratnk
fratnk

Reputation: 93

Your originaly problem was: You don't want to repeat yourself in several files. I suggest another approach to solve this problem: We don't you make a standard file, where you define your common states and import those states with the import statement described here: http://www.eclipse.org/Xtext/documentation/1_0_1/xtext.html#syntax

Upvotes: 1

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