Reference using a multivariable definition

[rhumbertgz]

Hello,

Could be possible to reference an object in the following oversimplified situation?

Line 1 defines three variables (x, y, z) of type "tello"
Line 2 the action 'go' reference one of the variables defined in l1

Example

l1  let x, y, z tello
l2 go x

Grammar

grammar HelloWorld

entry Model:
   (expression+=Expression)*;

Let: 'let' name+=ID (',' name+=ID)* type=('tello' | 'mbot');
Go: 'go' to=[Let:ID];

...

In this situation based on my current grammar definition I get an error saying that 'x' cannot be found.

Could be possible to reference a variable that was defined using the current syntax?

Best regards,
Humberto

[msujew]

Hey @rhumbertgz,

Langium is by default using a very simple lexical scoping mechanism (i.e. you can reference everything that is declared locally or in a parent of the current AST node). Since the Let and Go nodes probably live in different hierarchies, they can't see each other directly through the lexical scoping. So to fix this, you'll need to do the following:

1. First off, multiple names for single a element are not supported by default, but I believe you want to declare three separate elements anyway. So you'll need to refactor your Let rule slightly:

Let: 'let' variables+=Variable (',' variables+=Variable)* type=('tello' | 'mbot');
Variable: name=ID;

2. Tell the scope computation that you want to change the way your local scope mechanism works. We've just merged our scoping guide, where you'll find how to reference nodes from a different hierarchy using a fully qualified name. In your case, creating a FQN is not necessary, but you'll still need to override computeLocalScopes to create a local scope that not only incorporates the current element hierarchy but other elements as well.

Could be possible to reference a variable that was defined using the current syntax?

You'll need to modify your grammar slightly, but that shouldn't be too much of an issue. Most of the work will be in correctly computing the local scope for the Go.to reference.

[rhumbertgz]

Thank you for the explanation @msujew