visitListenExpr method

@override Object? visitListenExpr(Listen expr)

Implementation

@override
Object? visitListenExpr(Expr.Listen expr) {
  Object? object = evaluate(expr.stream);
  List<Object?> arguments = [];
  Map<Symbol, Object?> namedArguments = {};
  for (Expr.Expr argument in expr.arguments) {
    var arg = evaluate(argument);
    if (argument is Expr.NamedArgs) {
      Map args = arg as Map;
      namedArguments.addAll({Symbol(args.keys.first): args.values.first});
    } else {
      arguments.add(arg);
    }
  }
  Stmt.Functional then;
  var func = evaluate(expr.arguments.first);
  if (func is! LoxFunction) {
    throw RuntimeError(
        expr.name, "Only func can be used as Mapping function");
  } else {
    then = func.declaration;
  }
  Environment previous = environment;
  if (object is Stream) {
    return object.listen((value) {
      if (expr.arguments.first is! Expr.Anonymous) {
        previous = environment;
      }
      LoxFunction thenFun = LoxFunction(then, previous, false);
      thenFun.call(this, [value], {});
    }, onError: (err) {
      var onError = namedArguments[Symbol('onError')];
      if (onError != null) {
        LoxFunction onErrorFun = onError as LoxFunction;
        onErrorFun.call(this, [err], {});
      }
    }, onDone: () {
      var onDone = namedArguments[Symbol('onDone')];
      if (onDone != null) {
        LoxFunction onDoneFun = onDone as LoxFunction;
        onDoneFun.call(this, [], {});
      }
    });
  }
  throw RuntimeError(expr.name, "Only stream can be used in listen.");
}