Resolving cyclic dependencies between modules in Langium

[mrtnstn]

While working on a type system for my Langium language, I ran into this error message:
Cycle detected. Please make "TypeSystem" lazy. See https://langium.org/docs/di/cyclic-dependencies

It makes some sense to me, because I have both a TypeSystem and a TypeProvider module that depend on each other.

My question is how to resolve this? How do I make the module 'lazy', as suggested in the error message? If all else fails, I could consider to merge the two modules into one, but I would prefer to keep some separation of concerns.

The referenced documentation does not seem to be written yet :-(

[msujew]

Hey @mrtnstn,

sometimes cycles are unavoidable (we have some in our own framework). In order to make them lazy, you can do something like this:

class TypeSystem {
  private readonly provider: () => TypeProvider;
  constructor(services: TypeServices) {
    provider = () => services.TypeProvider; // <-- lazy evaluated service
  }
}

class TypeProvider {
  private readonly typeSystem: TypeSystem;
  constructor(services: TypeServices) {
    typeSystem = services.TypeSystem;
  }
}

[mrtnstn]

Thank you Mark for your speedy answer. That does the trick indeed. I'll see if I can find some time to write up that missing documentation.

[spoenemann]

There's an issue about writing the missing documentation page: eclipse-langium/langium-website#39