Monad transformer example using FSharpPlus

FSharpPlusTransformer.fs

#r "/Users/cowlike/.nuget/packages/fsharpplus/1.1.0-ci00271/lib/netstandard2.0/FSharpPlus.dll"  

open FSharpPlus
open FSharpPlus.Data

let doAsyncThing = async {return System.DateTime.Now}
let doNextAsyncThing (x:System.DateTime) = async {
    let m = x.Millisecond  
    return (if m < 500 then Some m else None)
    }

let f x = 2 * x
let run1 = monad {
    let! x = lift doAsyncThing
    let! y = OptionT (doNextAsyncThing x)
    return f y
    }

let doResultThing: Result<System.Random,string> = Ok <| System.Random()
let doNextResultThing (rand: System.Random): Result<int option,string> = monad {
    let r  = rand.Next(10)
    return (if r < 5 then Some r else None)
    }

let run2 = monad {
    let! x = lift doResultThing
    let! y = OptionT (doNextResultThing(x))
    return f y
    }

let run3 = monad {
    let realInt: Result<int option,string> = return (Some 1)
    let! x = OptionT realInt
    return x * 10 } 

OptionT.run run3 |> printfn "%A"

run3 >>= (fun p -> lift (return (p * 10))) 
|> OptionT.run
|> printfn "%A"
|> ignore

let run4 = monad {
    let realInt: Option<Result<int,string>> = Some (result 1)
    let! x = ResultT realInt
    return x * 10 }

run4 >>= (fun p -> lift (Some (p * 10)))
|> ResultT.run
|> printfn "%A"
|> ignore

Example using FSharpPlus, slightly extended example from this StackOverflow