XText establishing cross-references for a generic type

Question

This is what I want I am trying to parse

type Number(); // define a type called "Number" with no member variables
type Point(Number x, Number y); // define a type called Point with member variables

// and something with generic types
type Pair[T, V](T first, V second);

// and even something cyclic:
type LinkedList[T](T payload, LinkedList[T] rest);

And here's my xtext grammar that allows it:

TypeDecl returns SSType:
  'type' name=TypeName
  ('[' typeParams += TypeName (',' typeParams += TypeName)*  ']')?
  '(' (args += Arg (',' args += Arg)*)? ')' ';'
;

TypeName returns SSTypeName:
   name=ID
;

Type:
  tn = [SSTypeName] ('[' typeParams += Type (',' typeParams += Type)*  ']')?
;


Arg:
  type = Type argName = ID
;

Which works, but is way too liberal in what it accepts. If something is declared as a generic (eg the LinkedList in the above example) it should only be valid to use it as a generic (eg LinkedList[Number] and not LinkedList ) and ideally the arity of the type arguments would be enforced.

And of course, if something is declared to not be a generic type (eg Number), it shouldn't be valid to give it type arguments.

Example of stuff it will wrongly accept:

type Wrong1(Number[Blah] a); // number doesn't have type arguments
type Wrong2(Pair a); // Pair has type arguments
type Wrong3(Pair[Number, Number, Number] a); // wrong arity 

Any suggestions, comments, code or tips on how to do this properly would be much appreciated.

Answer 1

You should enforce the correct number of type arguments in your validator. It often better to have a liberal scope provider and a strict validator to provide better error messages.