first_attempt.fs

let private Main () =

    // traverse that works for 'get' only
    let traverse ((f1, f2): PLens<'a, 'b>): Lens<'a list, 'b list> =
        (fun x -> x |> List.map f1 |> List.choose id), 
        (fun _ -> fun x -> x) // this doesn't work

    let resourceMapLens =
        Json.ObjectPLens
        >??> mapPLens "links"
        <??> Json.ArrayPIso
        >?-> traverse (Json.ObjectPLens >??> mapPLens "href" <??> Json.StringPIso)

    let json = 
        @"{
            ""links"": [
                { ""href"": ""https://follow-the-links/"", ""rel"": ""purchase:baskets"" },
                { ""href"": ""https://follow-some-more/"", ""rel"": ""purchase:transactions"" }
            ]
        }"

    match Json.parse json |> Json.getLensPartial resourceMapLens with
    | Value value, _ -> 
        let result = sprintf "%A" value
        sprintf "%A" result
    | Error error, _ -> error

lens_over_list.fs

    let resourceMapLens =
        Json.ObjectPLens
        >??> mapPLens "links"
        <??> Json.ArrayPIso
        >??> traverse           // so apply the following lens to everything in the array
        <??> Json.ObjectPIso
        >??> mapPLens "href"
        <??> Json.StringPIso

    let json = 
        @"{
            ""links"": [
                { ""href"": ""https://follow-the-links/"", ""rel"": ""purchase:baskets"" },
                { ""href"": ""https://follow-some-more/"", ""rel"": ""purchase:transactions"" }
            ]
        }"

    match Json.parse json |> Json.getLensPartial resourceMapLens with
    | Value value, _ -> // value should be  a string list
    | Error error, _ -> // handle not found