Sanchime.Learn/Monads/Test.fs

namespace Sanchime.Monads

module Test =

    let reader_example () =

        let cache (Reader(f)) = (Reader (fun (v1, v2) ->
            match v1 with
            | None -> f v2
            | Some v -> v))

        let read s n = reader {
            printfn "读取：%s" s
            return n
        }

        let m = reader {
            let! a = cache <| read "A" 1
            let! b = cache <| read "B" 2
            let! c = read "C" 3
            return a + b + c
        }

        let (Reader f) = m

        f ((None, ()), ((None, ()), ((), ()))) |> ignore
        f ((Some 1, ()), ((None, ()), ((), ()))) |> ignore
        f ((None, ()), ((Some 2, ()), ((), ()))) |> ignore
        f ((Some 1, ()), ((Some 2, ()), ((), ()))) |> ignore