parseDomainType pure function example

NoteService.fs

module  NotesService
open Newtonsoft.Json
open System
open FSharp.Data

// This type was used for simplicty. 
type RestApiResponse = {
    StatusCode:int
    Body:string
    Headers: Map<string,string>
}

// In the real world, HttpResponse from Fsharp.Data is more usefult

// Custom error type
type RestApiError = 
| ServerError of response:string
| ClientError of response:string
| MalformedResponse of error:exn

// Our target type - yep we're building a notes apps :) 
type Note = {
    Created: DateTime
    Message: string
}

// This is using FSharp/Data's HttpResponse as the input. You could roll your own, as I 
// have shown at the top of the file and in the blog post. 
let inline parseDomainType<'a> (response: HttpResponse): Result<'a, RestApiError> = 

    let body = 
        match response.Body with
        | Binary b -> "" // Assuming this code will never need to handle binary data
        | Text t -> t

    match response.StatusCode with 
    | x when x >= 500 && x <= 599 -> body |> ServerError |> Error
    | x when x >= 400 && x <= 499 -> body |> ClientError |> Error
    | _ -> 
        try 
            body |> JsonConvert.DeserializeObject<'a> |> Ok
        with 
        | e -> e |> MalformedResponse |> Error