What is Iptscrae?

Iptscrae is the scripting language that Palace uses. The name comes from the pig latin for script. Iptscrae is what we computer geeks like to call a Reverse Polish Notation, or postfix language. The Iptscrae Command Reference talks about this to some detail. In a nutshell, iptscrae does things in reverse order than that of other scripting languages.

Remember how we talked about arguments and commands earlier? In iptscrae, you tell the language about the argument first, then give it the command. This is similar to telling your child "yard clean" or "room clean" For people who have scripted or programmed before, this takes some getting used to!

There are many technical reasons why iptscrae works this way. The one you as a scripter are concerned with is that of iptscrae's stack. Think of a stack as a pile of dishes. With me so far? Lets say you have three dishes, a red one, a green one and a blue one. Using our clean analogy before, how would you clean the green plate? green clean would be the answer. Some commands take several arguments though. How do we handle this case? Lets say we had a command named cleanthese, that cleaned all of the dishes you handed it.

Well the stack is like a pile of dishes. Lets say we take the red dish and set it on the counter:

red

Now lets say we set the blue plate on top of it:

blue

red

Now we have a pile of two dishes! If we now said "clean" then iptscrae would clean the blue dish, because its the top one on the stack. Iptscrae washes dishes just like you would! After that dish is washed and put away, we only have the red dish left. Telling iptscrae to "clean" again would then clean the red dish. What happens if we tell iptscrae to clean a third time? With the new Palace client, we will get an error, because there is nothing left to clean.

Now for some technical terms. Putting something onto the stack is called "pushing." Taking something off of the stack is called "popping." Iptscrae commands always work by popping their arguments off of the stack. Some commands require no arguments, some require one argument, some commands require several arguments.

Some commands even push their own data onto the stack! Lets look at our first real example, using the addition command, or + sign:

10 5 +

In this little bit of iptscrae, we first push the number 10 onto the stack. Then we push the number 5 onto the stack. Then we execute the addition command. Before the addition command executes, the stack looks like this:

5

10

After the addition command executes, the stack looks like this:

15

Whoa! What happened here? The addition command first pops off the 5. It next pops off the 10. Remember, popping off an argument is like taking a dish off the top of the dish stack to wash it, and you never put a clean plate back on a dirty pile! Now that addition has the two numbers it needs, it adds them up, gets the result of 15, then pushes that 15 back onto the stack.

Why does addition push the 15 onto the stack? This is done so you can use the result of the addition. You might store this result for later use, or you might use it immediately in a new command. Lets get a bit more complicated and see if you are still with us:

10 5 + 2 *

Jumping Jimmy! Whats that nonsense? Well its all rather simple if you just keep the dish stack concept in memory. First, 10 is pushed onto the stack, then 5 as before. Addition takes those two numbers off the stack (so we're out of dishes at the moment) and adds them. It then pushes the result, 15, onto the stack. Next we see a 2, which means to push it on the stack, so our stack now looks like:

2

15

Finally, we see the multiplication command, which indeed takes two arguments. It pops off the 2, then the 15, multiplies them, then pushes the result, 30, back onto the stack!

See how this all works? You push arguments that commands you want to use onto the stack, simply by declaring the value, such as 2. You then declare the command and it executes. All you need to know is what command you want to use and what arguments that command expects to see on the stack.

How big is this stack of dishes you ask? It can get fairly large, but its a wise idea to try and keep the stack small. As the stack grows it does require more of the computers memory to keep track of whats in that stack, so use it wisely.

Next we will talk about the different kind of arguments, or dishes, we can have on the stack.

Last Updated on 03/08/2000