LangExt.Guard.cs

using System;
using System.Collections.Generic;
using System.Text;
using System.Threading.Tasks;
using LangExt;

namespace LangExt.Guard
{
    public static class Control
    {

        public static Result<TSuccess, TFailure> Guard<TSuccess, TFailure>(this Result<Placeholder, TFailure> it, bool cond, TFailure failure)
        {
            if (cond) return it;
            else return ((Result<TSuccess, TFailure>)it).Bind(m => Result.Failure(failure));
        }

        public static Result<TSuccess, TFailure> Guard<TSuccess, TFailure>(this Result<TSuccess, Placeholder> it, bool cond, TFailure failure)
        {
            if (cond) return it;
            else return ((Result<TSuccess, TFailure>)it).Bind(m => Result.Failure(failure));
        }

        public static Result<TSuccess, TFailure> Guard<TSuccess, TFailure>(this Result<TSuccess, TFailure> it, bool cond, TFailure failure)
        {
            if(cond) return it;
            else return it.Bind(m => Result.Failure(failure));
        }

        public static Result<TSuccess, TFailure> Unless<TSuccess, TFailure>(this Result<Placeholder, TFailure> it, bool cond, TFailure failure)
        {
            return it.Guard(!cond, failure);
        }

        public static Result<TSuccess, TFailure> Unless<TSuccess, TFailure>(this Result<TSuccess, Placeholder> it, bool cond, TFailure failure)
        {
            return it.Guard(!cond, failure);
        }

        public static Result<TSuccess, TFailure> Unless<TSuccess, TFailure>(this Result<TSuccess, TFailure> it, bool cond, TFailure failure)
        {
            return it.Guard(!cond, failure);
        }

        public static Option<T> Guard<T>(this Option<T> it, bool cond)
        {
            return cond ? it : it.Bind(m => Option.None);
        }
        
        public static Option<T> Unless<T>(this Option<T> it, bool cond)
        {
            return it.Guard(!cond);
        }

        public static Option<Unit> When(bool cond)
        {
            return cond ? Option.Some() : Option.None;
        }
    }


    class Program
    {
        static void Main(string[] args)
        {
            var result = 
                Result.SuccessLazy(() => "succ")
                .Guard(true, -1)
                .Guard(true, -2)
                .Guard(true, () => -3)
                .Unless(true, -4);

            var result2 = 
                Result.Failure(-1)
                .Guard(true,  -1)
                .Guard(false, -2)
                .Guard(false, -3)
                .Unless(true, -4);

            var opt =
                Option.Some("a")
                .Guard(true);
        }
    }
}