/* e.g.

  overlay <- ScreenOverlay
  bounds <- rightScreenBounds
  overlay bounds bounds
  overlay show
*/
  
// We're using SynchronizedList as a list wrapper
sclass GazelleV_LeftArrowScript extends SynchronizedList<GazelleV_LeftArrowScript.Evaluable> is GazelleV_LeftArrowScript.Evaluable {
  interface Evaluable {
    public O get(VarContext ctx default new);
  }
  
  *() { super(new L); }
  
  public O get(VarContext ctx) {
    O result = null;
    for (step : this)
      result = step.get(ctx);
    ret result;
  }
  
  toString { ret pnlToLines(this); }

  srecord noeq FunctionDef(S name, LS args, Evaluable body) {}
  
  srecord noeq Assignment(S var, Evaluable expression) is Evaluable {
    public O get(VarContext ctx) {
      O o = expression.get(ctx);
      ctx.set(var, o);
      ret o;
    }
    
    toString { ret var + " <- " + expression; }
  }
  
  persistable sclass NewObject is Evaluable {
    Class c;
    L<Evaluable> args;
    
    *(Class *c) {}
    *(Class *c, L<Evaluable> *args) {}
    
    public O get(VarContext ctx) {
      ret callConstructor(c, mapToArray(args, arg -> arg.get(ctx)));
    }
    
    toString { ret "new " + formatFunctionCall(className(c), args); }
  }
  
  srecord noeq CallFunction(FunctionDef f, L<Evaluable> args) is Evaluable {
    public O get(VarContext ctx) {
      var ctx2 = new VarContext(ctx);
      for (S declared, Evaluable actual : unpair zipLists(f.args, args))
        ctx2.put(declared, actual.get(ctx));
      print ifdef GazelleV_LeftArrowScript_debug(ctx2 := ctx2.vars);
      ret f.body.get(ctx2);
    }
    
    toString { ret formatFunctionCall(f.name, args); }
  }
  
  srecord noeq GetVar(S var) is Evaluable {
    public O get(VarContext ctx) {
      ret ctx.get(var);
    }
    
    toString { ret var; }
  }
  
  srecord noeq Const(O value) is Evaluable {
    public O get(VarContext ctx) {
      ret value;
    }
    
    toString { ret strOrClassName(value); }
  }
  
  srecord CallMethod(Evaluable target, S methodName, L<Evaluable> args) is Evaluable {
    public O get(VarContext ctx) {
      ret call(target.get(ctx), methodName, mapToArray(args, arg -> arg.get(ctx)));
    }
    
    toString { ret target + "." + formatFunctionCall(methodName, args); }
  }
}

Began life as a copy of #1033981