visitThenExpr method

Implementation

@override
Object? visitThenExpr(Expr.Then expr) {
  Object? object = evaluate(expr.future);
  if (object is Future) {
    Stmt.Functional then;
    var func = evaluate(expr.then);
    if (func is! LoxFunction) {
      throw RuntimeError(
          expr.name, "Only func can be used as Mapping function");
    } else {
      then = func.declaration;
    }
    Environment previous = environment;
    return object.then((value) {
      if (expr.then is! Expr.Anonymous) {
        previous = environment;
      }
      LoxFunction thenFun = LoxFunction(then, previous, false);
      return thenFun.call(this, [value], {});
    });
  }
  throw RuntimeError(expr.name, "Only future can be used in then.");
}