/* 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); }

  }

}