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Loops

Perform an action multiple times based on a boolean condition, checked before the first action (WHILE .. DO)

Starting with a variable x=1, Print the sequence "1,2,4,8,16,32,64,128," by doubling x and checking that x is less than 150.
erlang
X = 1, print_while_X_less_150(X).
Pred = fun (X) -> X < 150 end,
Action = fun (X) -> io:format("~B,", [X]), X * 2 end,
X = 1,

while_do(Pred, Action, X).
fsharp
let mutable x = 1
while x < 150 do printf "%d, " x ; (x <- x * 2) done
// The problem is clearly geared towards imperative languages ;-)
// No need to mutate any variable, here's how to do it loop-free functional:
let rec powers2 i = seq { if i < 150 then yield i; yield! powers2 (i*2) }
powers2 1 |> Seq.iter (fun i -> printf "%i, " i)
fantom
x := 1
while (x < 150) {
Env.cur.out.print("$x,")
x *= 2
}
echo

Perform an action multiple times based on a boolean condition, checked after the first action (DO .. WHILE)

Simulate rolling a die until you get a six. Produce random numbers, printing them until a six is rolled. An example output might be "4,2,1,2,6"
erlang
Pred = fun (DiceRoll) -> DiceRoll =/= 6 end,
Action = fun (DiceRoll) -> io:format("~B,", [DiceRoll]), dice_roll() end,

do_while(Pred, Action, dice_roll()).
-module(dice).
-export([start/0]).

start() ->
roll(dice_roll()).

roll(6) ->
io:format("6~n", []);
roll(N) ->
io:format("~B,", [N]),
roll(dice_roll()).

dice_roll() -> random:uniform(6).
fsharp
open System
let rand = Random()

Seq.initInfinite (fun _ -> rand.Next(1, 7))
|> Seq.takeWhile (fun x -> x < 6)
|> fun items -> String.Join(",", items)
|> function s when s = "" -> printfn "6" | s -> printfn "%s,6" s
fantom
rnd := 0
while(rnd != 6) {
rnd = Int.random(1..6)
Env.cur.out.print(rnd)
if (rnd != 6)
Env.cur.out.print(",")
}
echo

Perform an action a fixed number of times (FOR)

Display the string "Hello" five times like "HelloHelloHelloHelloHello"
erlang
dotimes(5, fun () -> io:format("Hello") end).
lists:foreach(fun (_) -> io:format("Hello") end, lists:seq(1, 5)).
fsharp
for i = 1 to 5 do printf "Hello" done
dotimes 5 (fun () -> printf "Hello")
// Repetition via ranging over a List type(index ignored)
for _ in list do printf "Hello" done
// Repetition via ranging over a Sequence type(index ignored)
for _ in sequence do printf "Hello" done
// Repetition via ranging over an Array type(index ignored)
for _ in array do printf "Hello" done
fantom
5.times { Env.cur.out.print("Hello") }
for (i := 0; i < 5; i++)
Env.cur.out.print("Hello")
(1..5).each { Env.cur.out.print("Hello") }

Perform an action a fixed number of times with a counter

Display the string "10 .. 9 .. 8 .. 7 .. 6 .. 5 .. 4 .. 3 .. 2 .. 1 .. Liftoff!"
erlang
fromto(10, 1, -1, fun (X) -> io:format("~B .. ", [X]) end), io:format("Liftoff!~n").
lists:foreach(fun (X) -> io:format("~B .. ", [X]) end, lists:seq(10, 1, -1)), io:format("Liftoff!~n").
fsharp
for i = 10 downto 1 do printf "%d .. " i done
printfn "Liftoff!"
// Repetition via ranging over a Sequence type
for i in {10 .. -1 .. 1} do printf "%d .. " i done ; printfn "Liftoff!"
fantom
(10..1).each { Env.cur.out.print("$it .. ") }
Env.cur.out.print("Liftoff!")
for (i := 10; i >= 1; i--)
Env.cur.out.print("$i .. ")
Env.cur.out.print("Liftoff!")