F#：我需要将我的输出格式化为仅包含逗号分隔的整数，而不是 F# 中的列表格式

Question

I have a function that takes a list of Integer values and returns the same. In the body of the function I need it to print out the output list before returning it. Currently it prints out the output below. I would like to print the items in the list out separated by commas without using any type of loop.

My output currently looks like: Even numbers : [8; 10; 12; 14] Even numbers : [8; 10; 12; 14]

My desired output formatting looks like: Even numbers : 8 10 12 14

let evens_only (x : List<Int32>) : List<Int32> =
    let output_list = x |> List.filter(fun y -> (y % 2) = 0)
    printfn "Even numbers : %A" output_list
    output_list

Answer 1

Just map printf over the list ( List.iter is similar to List.map in its functionality for this example).

let evens_only (x : List<Int32>) : List<Int32> =
    let output_list = x |> List.filter(fun y -> (y % 2) = 0)
    printf "Even numbers : "
    List.iter (fun i -> printf "%i " i) output_list
    printfn "" //extra newline
    output_list

Output:

> evens_only [8; 10; 12; 14];;
Even numbers : 8 10 12 14 
val it : List<Int32> = [8; 10; 12; 14]