One more HR F# challenge for today - Hello World N Times:

Print "Hello World" N amount of times. ... A single line of input containing integer N, the number of times to print "Hello World".

The iterative process in F# can be constructed in three ways:

  • the well-known for loop
  • the sequence generator
  • recursion

There are three implementations that demonstrates each of these three approaches:

// using loop to iterate over the range
let printHello1 n =
  for _ in 1..n do
    printn "Hello World"

// generate sequence and invoke function for each item
let printHello2 n =
  seq { 1 .. n }
  |> Seq.iter (fun _ -> printfn "Hello World")

// call itself recursively until end
let rec printHello3 n =
  match n with
  | 0 -> ()
  | _ -> printfn "Hello World"
         printHello3 (n-1)

Without tail recusrion optimisation enabled the printHello3 function drains stack memory for large n.

The complete for-loop solution:

open System

let printHello n =
  for _ in 1..n do printfn "Hello World"

[<EntryPoint>]
let main argv = 
    Console.ReadLine()
    |> int
    |> printHello
    0 // return an integer exit code