A keyword is a special word that has been taken for the program, so we can't use it in our own as the name of a variable, function, etc.
We’ve covered the majority of the Lua keywords, but there are a few left that we have to cover. We’ll cover the final keywords that aren’t loop/table-based in this tutorial, and we’ll cover tables and loops in the next! We only have three to touch on.
If, Elseif, Else
So, we’ve seen conditional statements – if these things, then do this. But we haven’t covered their full usage!
First things first – if you want stuff to happen based on a condition, you use that word I just used twice –
local var = 5 if var == 5 then -- [[ do stuff ]] end
then defines a new scope here, and that scope ends at, well,
end. The conditional is the statement between
local var = 5 function example() if var == 5 then -- if var is equivalent to 5 then... out("This is 5!") return end out("Not 5!") end example() → This is 5! var = 10 example() → Not 5!
In this example, we’re checking whether var is
5. If it is, we print “This is 5!”; if it isn’t, we print “Not 5!”. We prevent the printing of both of them by using the
return – otherwise, if the var were
5, both outs would be called.
We can also do this by using the
local var = 5 function example() if var == 5 then out("This is 5!") else out("Not 5!") end end example() → This is 5! var = 10 example() → Not 5!
Functionally, exactly the same. However, it’s prettier to look at, and makes more sense to read. Do note that
else also creates its own scope; in this instance, there is a scope between
else; and another between
What if we wanted to check for more than one specific condition? We can use
local var = 5 function example() if var == 5 then out("This is 5!") elseif var == 7 then out("This is 7!") else out("Not 5 or 7!") end end example() → This is 5! var = 7 example() → This is 7! var = 10 example() → Not 5 or 7!
We can use more than one elseif, too. Only one
else within that block between
if and the first
Do keep in mind that whichever “path” works first is the one that will be used, and the ones following it will be ignored, until the
end of the conditional.
local var = 10 function example() if var > 5 then out("This is greater than 5!") elseif var == 5 then out("This is 5!") elseif var == 7 then out("This is 7!") else out("Less than 5, not 7!") end end example() → This is greater than 5! var = 5 example() → This is 5! var = 7 example() → Less than 5, not 7!
Even though the var matches the second conditional statement –
var == 7 – for the final assignment, it also matches the first condition, so that’s the one and only path the code takes here.
Do note that you can do just one if and elseif, or an if and an else, or all three, or just an if, or like twenty elseif’s. Though that’s bad code, don’t do that.
End, Then, Do
end is needed to denote the end of a scope, when that scope is defined by something other than the entire file. Each of the following keywords need an
end to finish their scope:
And the keyword
then is needed after the conditional statement for an
do is used in two instances; one, to create a new scope without needing any other keywords (see example below).
local var = 5 do local var = 10 out(var) → 10 end out(var) → 5
The other, and more common, usage of
do is to attach it to loop keywords. Read on to the next chapter!