Parser.OfType.cs

namespace Pidgin
{
    public abstract partial class Parser<TToken, T>
    {
        /// <summary>
        /// Creates a parser which casts the return value of the current parser to the specified result type, or fails if the return value is not an instance of <typeparamref name="U"/>.
        /// </summary>
        /// <typeparam name="U">The type to cast the return value of the current parser to</typeparam>
        /// <returns>A parser which returns the current parser's return value casted to <typeparamref name="U"/>, if the value is an instance of <typeparamref name="U"/></returns>
        public Parser<TToken, U> OfType<U>()
            => this
                .Assert(x => x is U, x => $"Expected a {typeof(U).Name} but got a {x.GetType().Name}")
                .Cast<U>()
                .Labelled($"result of type {typeof(U).Name}");
    }
}