Where are m and n coming from here?

I've put the function definition in the header section. I don't know if this is allowed or not. I see a lot of people doing that, putting only the relevent part/expression in the code section.

Here is the full function, 78 bytes:

function f(m,n)for i=0,m*n-1 do _=(i%n==0)and print()or io.write(i,' ')end end

Oh, I see. I'll add this in a Meta post later, but the main rules for function submissions are as follows: You need to have all the code that is necessary to create the function within your submission. Some languages have first class functions, so they can just put the value in a submission and ask me to assign it in order to use it more than once. If Lua has such a thing, you can use it without reservation. If there are some other answers which are incorrect in the same way, please link them here. I'll have to add comments on them as well.

If Lua has such a thing, you can use it without reservation.

I guess yes. If you call this a first-class function:

f = function(m,n)for i=0,m*n-1 do _=(i%n==0)and print()or io.write(i,' ')end end

So I will use it from now onwards.

I'll add this in a Meta post later, but the main rules for function submissions are as follows: You need to have all the code that is necessary to create the function within your submission.

Please make sure that this will apply to all challenges.