please include function plus.

svoid test_lasTypeSpecialization() {
  new GazelleV_LeftArrowScriptParser parser;
  parser.allowTheWorld();
  parser.addVar("i", new LASValueDescriptor.Exact(int.class, false));
  var script = parser.parse("plus i i");
  printIndentedStruct(script);
  var step = first(script.steps);
  print(returnType := step.returnType());
  var opt = step.optimize();
  print(optimized := opt);
  assertInstanceOf(opt, GazelleV_LeftArrowScript.DirectMethodCallOnKnownTarget.class);
  print(returnType := opt.returnType());
  
  new FlexibleVarContext ctx;
  ctx.put(i := 5);
  assertEqualsVerbose(10, opt.get(ctx));
}