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Structure
Conditionals

Perform an action if a condition is true (IF .. THEN)

Given a variable name, if the value is "Bob", display the string "Hello, Bob!". Perform no action if the name is not equal.
fantom
if (name=="Bob") echo("Hello, Bob!")
erlang
if (Name == "Bob") -> io:format("Hello, ~s!~n", [Name]) ; true -> false end.
case Name of "Bob" -> io:format("Hello, ~s!~n", [Name]) ; _ -> false end.
Name == "Bob" andalso (begin io:format("Hello, ~s!~n", [Name]), true end).
fsharp
if name = "Bob" then printfn "Hello, %s!" name
name = "Bob" && begin printfn "Hello, %s!" name ; true end

Perform different actions depending on a boolean condition (IF .. THEN .. ELSE)

Given a variable age, if the value is greater than 42 display "You are old", otherwise display "You are young"
fantom
if (age > 42)
echo("You are old")
else
echo("You are young")
echo((age > 42) ? "You are old" : "You are young")
erlang
if Age > 42 -> io:format("You are old~n") ; true -> io:format("You are young~n") end.
Message = if Age > 42 -> "old" ; true -> "young" end, io:format("You are ~s~n", [Message]).
case Age > 42 of true -> io:format("You are old~n") ; false -> io:format("You are young~n") end.
case Age of _ when Age > 42 -> io:format("You are old~n") ; _ -> io:format("You are young~n") end.
Message = case Age of _ when Age > 42 -> "old" ; _ -> "young" end, io:format("You are ~s~n", [Message]).
Age > 42 andalso (begin io:format("You are old~n"), true end) orelse (begin io:format("You are young~n"), true end).
(fun (X) when X > 42 -> io:format("You are old~n"); (_) -> io:format("You are young~n") end)(Age).
(fun () when Age > 42 -> io:format("You are old~n"); () -> io:format("You are young~n") end)().
io:format("You are ~s~n", [if Age > 42 -> "old" ; true -> "young" end]).
fsharp
if age > 42 then printfn "You are old" else printfn "You are young"
let message = if age > 42 then "old" else "young"
printfn "You are %s" message

Perform different actions depending on several boolean conditions (IF .. THEN .. ELSIF .. ELSE)

fantom
if (age > 84)
echo("You are really ancient")
else if (age > 30)
echo("You are middle-aged")
else
echo("You are young")
erlang
if
Age > 84 -> io:format("You are really ancient~n");
Age > 30 -> io:format("You are middle-aged~n");
true -> io:format("You are young~n")
end.
case Age of
_ when Age > 84 -> io:format("You are really ancient~n");
_ when Age > 30 -> io:format("You are middle-aged~n");
true -> io:format("You are young~n")
end.
fsharp
if age > 84 then printfn "You are really ancient"
elif age > 30 then printfn "You are middle-aged"
else printfn "You are young"
let message = match age with
| _ when age > 84 -> "really ancient"
| _ when age > 30 -> "middle-aged"
| _ -> "young"
printfn "You are %s" message

Replacing a conditional with many branches with a switch/case statement

Many languages support more compact forms of branching than just if ... then ... else such as switch or case or match. Use such a form to add an appropriate placing suffix to the numbers 1..40, e.g. 1st, 2nd, 3rd, 4th, ..., 11th, 12th, ... 39th, 40th
fantom
suffix := |Int n -> Str|
{
if ((4..20).contains(n % 100))
return "th"

switch((n.toStr)[-1])
{
case '1': return "st"
case '2': return "nd"
case '3': return "rd"
default: return "th"
}
}

(1..40).each { echo("$it${suffix(it)}") }
erlang
Suffix = case Num of
N when N > 10, N < 20 -> "th";
N when N rem 10 =:= 1 -> "st";
N when N rem 10 =:= 2 -> "nd";
N when N rem 10 =:= 3 -> "rd";
_ -> "th"
end,
io_lib:format("~w~s", [Num, Suffix])
fsharp
let suffix = function
| n when n > 10 && n < 20 -> "th"
| n when n % 10 = 1 -> "st"
| n when n % 10 = 2 -> "nd"
| n when n % 10 = 3 -> "rd"
| _ -> "th"

seq { 1 .. 40 }
|> Seq.iter (fun n -> printfn "%i%s" n (suffix n))
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.
fantom
x := 1
while (x < 150) {
Env.cur.out.print("$x,")
x *= 2
}
echo
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)

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"
fantom
rnd := 0
while(rnd != 6) {
rnd = Int.random(1..6)
Env.cur.out.print(rnd)
if (rnd != 6)
Env.cur.out.print(",")
}
echo
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

Perform an action a fixed number of times (FOR)

Display the string "Hello" five times like "HelloHelloHelloHelloHello"
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") }
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

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!"
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!")
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!"