f# - 計算式でカスタム演算子を定義する方法

Question

計算式にいくつかのカスタム演算子を定義したいのですが、うまくいきません

type ZipSeq() =

    [<CustomOperation("<*>")>]
    member this.Apply f s = 
        f |> Seq.zip s |> Seq.map (fun (y, x) -> x(y))

    member this.Return x = 
        Seq.initInfinite (fun _ -> x)

    // (a -> b) -> seq<a> -> seq<b>
    [<CustomOperation("<!>")>]
    member this.Map f s =
        this.Apply (this.Return f) s

let zipSeq = new ZipSeq()

let f (a : float) = a * a
let s = seq { yield 1. }

// seq<b>
let h1 = zipSeq.Map f s

//thinking h1 should be the same as h2
//but compilation error : ` This value is not a function and cannot be applied`
let h2 = zipSeq { return f <!> s }

ところで、に変更member this.Map f s ...しmember this.Map (f, s) ...ても同じエラーが発生します。