F# 对随机整数列表进行选择排序

Question

I am new to F# and trying to figure out some basics but am stumbling along slowly. In the code below I am trying to generate a list of random integers and then sorting it.

let randomNumberList count =
    let r = System.Random()
    List.init count (fun _ -> r.Next(100))

let rec selectionSort l = function
    | [] -> []
    | l -> let min = List.min l in
           let rest = List.filter (fun i -> i <> min) l in
           let sortedList = selectionSort rest in
           min :: sortedList
sortedList = selectionSort l

let unsortedList = randomNumberList 10
printfn "%A" unsortedList
printfn "%A" sortedList

So two things...one is the error I'm getting:

stdin(515,19): error FS0001: This expression was expected to have type
    'a list    
but here has type
    'a list -> 'a list

The other is with the random number list. It works, but I want the numbers generated to be less than 100, instead of the massive values I'm getting now.

Thanks for your patience and help!

Answer 1

As mentioned in the comment, there is no need for l in let rec selectionSort . Fixed code:

let randomNumberList count =
    let r = System.Random()
    List.init count (fun _ -> r.Next(100))

let rec selectionSort = function
    | [] -> []
    | l -> let min = List.min l in
           let rest = List.filter (fun i -> i <> min) l in
           let sortedList = selectionSort rest in
           min :: sortedList

let unsortedList = randomNumberList 10
let sortedList = selectionSort unsortedList
printfn "%A" unsortedList
printfn "%A" sortedList
System.Console.ReadLine() |> ignore

Explanation:

let vname = function
   | ... -> ...
   | ... -> ...

is the short form of

let vname arg = match arg with
   | ... -> ...
   | ... -> ...