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Concepts and Basics

This part will explain you how the Lua actually works inside the OS and help you to figure out what you’re doing when you write a script for the TI-Nspire. It is recommended to have some basics on Lua programming or some knowledge of event-driven languages, but keep in mind that it is not required.

The Lua is an interpreted script language which means that it isn’t as fast as ASM/C programs, but is still better than the TI-BASIC. One good thing is that this language is in a complete harmony with the OS with basic events and a powerful graphic context.

Lua is normally a sequential script language. For example, when we use the print() command to display a value, we can easily guess when the command will be run in the script. Here’s an example :

a = 1
print(a)
a = a + 1
print(a)

Output :

1
2

Nothing special. However, on the TI-Nspire, Lua has a completely different approach. We meet this approach with high-level programming or with object-oriented languages (like C++, C#, …). In those languages, we don’t have the ability to control the flow/execution of any function. Yes, it can be quite strange to hear that, but it’s the way it is. Are we going to learn a language that doesn’t do what we tell it to do ? Well, in a way, yes.

But don’t worry ! We’re here to learn how to cross this quite unstable bridge ! A wonderful world is on the other side.

First of all, you have to “change team”. As in before, you were the boss, this means you used to tell the machine to compute 1 + 1 and it would proudly output “2”. Now, you are a worker. A task authorization is given to you, thus, you explain to the machine how to do this work. Actually, those “authorizations” are called events. When the event is called, you can do what ever you want. Here is a pseudo-code explaining what to do when the “Cook” event is called :

function FaireLaCuisine()
	organiserLaPaillasse()
	couperLesIngredients()
	assembler()
	chauffer()
	servir()
end

You can easily understand that you won’t cook when you get the job. You’ll wait for your boss’ order ! Well, it is exactly the same thing between the TI-Nspire and you. But this time, the TI-Nspire framework is the boss. Everything is event-based.

In a nutshell, our functions have to be called by the TI-Nspire. But how to be sure that they will be executed ? It is the moment to look at the Events list. When an event is fired, the TI-Nspire gives zero, one or multiple parameters (“arguments”) that we can use in our function. This lets us know, for example, which key has been pressed, because when the TI-Nspire executes the charIn(ch) event, it gives also a string as an argument corresponding to the key. However, when the enterKey() event is fired, no argument is given.

Before, in a non-event-based language (like BASIC, C, PHP …) we used to program like this :

-- Initialisation des constantes ici
...
 
k = 0
while k != 0 do
	k = getKey()
end
if k == 72 then
	-- quelque chose
end

Now, it looks like that :

-- Initialisation des constantes ici
...
 
function on.charIn(ch)
    if ch == "7" then
	-- quelque chose
    end
end

We hope you understood that very important part…

 

Let’s go to Part 2 now !