未定义F# tryHead

let myList = [1; 2; 3]
let headOrDefault = List.tryHead myList

match headOrDefault with
| Some(value) -> printfn "The head element is: %d" value
| None -> printfn "The list is empty."

let mySequence = seq { 1 .. 3 }
let headOrDefault = Seq.tryHead mySequence

match headOrDefault with
| Some(value) -> printfn "The head element is: %d" value
| None -> printfn "The sequence is empty."

let tryHead (collection: 'a seq) : 'a option =
    collection |> Seq.tryPick (fun x -> Some x)

let myList = [1; 2; 3]
let headOrDefault = tryHead myList

match headOrDefault with
| Some(value) -> printfn "The head element is: %d" value
| None -> printfn "The collection is empty."