Simulate (rather, just "write down") the Monty Hall problem.

monty-hall-prob.jl

function onegame()
    doors = (1,2,3)
    # drop(i::Int) = i == 1 ? (2,3) : i == 2 ? (1,3) : (1,2)
    
    true_ans = rand(doors)

    player1_ans = first_ans = rand(doors)

    if first_ans == 1
        if true_ans == 1
            # open = rand(drop(1))
            # [...]
            return false # player1 wins
        elseif true_ans == 2
            open = 3
            player2_ans = 2
            return true # player2 wins
        else
            open = 2
            player2_ans = 3
            return true # player2 wins
        end
    elseif first_ans == 2
        if true_ans == 1
            open = 3
            player2_ans = 1
            return true # player2 wins
        elseif true_ans == 2
            # open = rand(drop(2))
            # [...]
            return false # player1 wins
        else
            open = 1
            player2_ans = 3
            return true # player2 wins
        end
    else
        if true_ans == 1
            open = 2
            player2_ans = 1
            return true # player2 wins
        elseif true_ans == 2
            open = 1
            player2_ans = 2
            return true # player2 wins
        else
            # open = rand(drop(3))
            # [...]
            return false # player1 wins
        end
    end
end

let n = 1000000
    sum(onegame() for i = 1:1000000) / n # => 0.666129
end