anchor.diff:        var gen = emitGeneratorFn(jsParams);
         if (jsParams.isNotEmpty) gen = js.call('() => #(#)', [gen, jsParams]);
   
  -      var syncIterable = _emitType(syncIterableType.instantiate([returnType]));
  +      var syncIterable = _emitType(
  +        syncIterableElement.instantiate(
  +          typeArguments: [returnType],
  +          nullabilitySuffix: NullabilitySuffix.star,
  +        ),
  +      );
         return js.call('new #.new(#)', [syncIterable, gen]);
       }
   
  
positive.code:     var typeArgs = type.typeArguments;
      if (typeArgs.isEmpty) return _emitType(type);
      identity ??= jsTypeRep.isPrimitive(typeArgs[0]);
      type = identity ? identityHashMapImplType : linkedHashMapImplType;
      return _emitType(type.instantiate(typeArgs));
    }
  
    js_ast.Expression _emitConstSet(
  
negative.code:       var asyncStarParam = js_ast.TemporaryId('stream');
        var gen = emitGeneratorFn([asyncStarParam], asyncStarParam);
  
        var asyncStarImpl = asyncStarImplElement.instantiate(
          typeArguments: [returnType],
          nullabilitySuffix: NullabilitySuffix.star,
        );
        return js.call('new #.new(#).stream', [_emitType(asyncStarImpl), gen]);
      }
  
  