F＃不同类型的遍历列表

Question

I have five different types:

type Name        = string
type PhoneNumber = int
type Sex         = string
type YearOfBirth = int
type Interests   = string list
type Client      = Name * PhoneNumber * Sex * YearOfBirth * Interests

Which represent clients. Then let's say I have three of these clients:

let client1 = "Jon", 37514986, "Male", 1980, ["Cars"; "Sexdolls"; "Airplanes"]
let client2 = "Jonna", 31852654, "Female", 1990, ["Makeup"; "Sewing"; "Netflix"]
let client3 = "Jenna", 33658912, "Female", 1970, ["Robe Swinging"; "Llamas"; "Music"]
let clients = [client1; client2; client3]

How would I go about searching through clients for a certain element? Say, I have a method where I want to get the names of the clients with the same sex as me? I've written the below function for at least determining whether the input sex is the same but that doesn't cut it apparently.

let rec sexCheck sex cs = 
match cs with
| [] -> []
| c::cs -> if sex = c then sex else sexCheck sex cs

sexCheck "Male" clients

Any hints?

Answer 1

You can accumulate the results in another parameter, like this:

let sexCheck sex cs = 
    let rec loop acc (sex:string) cs = 
        match cs with
        | [] -> acc
        | ((_, _, s, _, _) as c)::cs -> loop (if sex = s then c::acc else acc) sex cs
    loop [] sex cs

As usual, I would like to remind you what's the easiest way, by using the provided functions in F#:

clients |> List.filter (fun (_, _, c, _, _) -> c = "Male")