/* e.g.

  overlay <- ScreenOverlay
  bounds <- rightScreenBounds
  overlay bounds bounds
  overlay show
*/

sclass GazelleV_LeftArrowScriptParser > SimpleLeftToRightParser {
  replace Toolbox with GazelleV_LeftArrowScript.
  delegate Script to Toolbox.
  delegate Evaluable to Toolbox.
  
  new Script script;
  new LinkedHashSet<S> knownVars;
  
  // object can be a class
  srecord MethodOnObject(O object, S method) {}
  
  Script parse(S text) {
    setText(text);
    while (mainLoop()) {
      S t = token();
      if (isIdentifier(t) && eq(token(1), "<") && eq(token(2), "-")) {
        next(3);
        knownVars.add(t);
        script.add(new Toolbox.Assignment(t, parseExpr()));
      } else
        script.add(parseExpr());
    }
    ret script;
  }
  
  Evaluable parseOptionalExpression() {
    if (lineBreak()) null;
    ret parseExpr();
  }
  
  Evaluable parseExpr() {
    if (atEnd()) null;
    S t = tpp();
    print(+t);
    
    if (knownVars.contains(t))
      ret parseCall(new Toolbox.GetVar(t));
      
    O o = findExternalObject(t);
    if (o == null)
      fail("Unknown object: " + t);
    else if (o cast Class)
      ret new Toolbox.NewObject(o);
    else if (o cast MethodOnObject)
      ret new Toolbox.CallMethod(new Toolbox.Const(o.object), o.method, parseExpressions());
    else
      ret parseCall(new Toolbox.Const(o));
  }
  
  L<Evaluable> parseExpressions() {
    ret collectWhileNotNull(-> parseOptionalExpression());
  }
  
  Evaluable parseCall(Evaluable target) {
    if (atEndOrLineBreak()) ret target;
    
    S methodName = tpp();
    var args = parseExpressions();
    ret new Toolbox.CallMethod(target, methodName, args);
  }
  
  // can return MethodOnObject
  swappable O findExternalObject(S name) { null; }
  
  void allowTheWorld(Class... functionContainers) {
    findExternalObject = name -> {
      Class c = findClassThroughDefaultClassFinder(name);
      if (c != null) ret c;
      fOr (container : functionContainers)
        if (hasMethodNamed(container, name))
          ret new MethodOnObject(container, name);
      null;
    };
  }
}