What's wrong with my lua?

Question

My first foray into lua, and this just doesn't work. It says that I'm trying to call global exiter (a nil value). I'm just doing a simple program to try and get functions to work.

print("hello world")
io.read()
y = 0

while y < 10 do
    local x = ""
    print("hello world")
    x = io.read()
    if x == "y" then
    y = exiter(1)
    print(y)
    end
end

function exiter(param)
    local q = 0
    print ("hello again")
    q = param * 10
    return q;
end

Answer 1

Lua programs are executed top-to-bottom, statement-by-statement. So, when you enter while loop, the function exiter has not come into existence yet. Define it before going into the loop:

function exiter(param)
    local q = 0
    print ("hello again")
    q = param * 10
    return q;
end

while y < 10 do
    local x = ""
    print("hello world")
    x = io.read()
    if x == "y" then
        y = exiter(1)
        print(y)
    end
end

Answer 2

Function definitions occur when the code for them is run. You aren't creating the exiter function until after you try to call it in the while loop. Reverse the order of your loop and function definition.