Language

Language basics

The language used in Pry with AI is called GameLoops. A game consists of one more game loops, and each game loops contains one or more commands, possibly with arguments, like:

DISPLAY "Hello world!"

By convention command names are written with capitals. All command arguments should be quoted, being formally strings of characters (texts).

Stack

The key concept in GameLoops is a global stack. Some commands can "return" values, and in such a case they push a value at the top of the stack. Like:

PROMPT "Tell me your name:"

asks the player for their name, and puts them at the top of the stack (denoted %1). So, assuming that the player answered "John", the stack will look like:

%1 "John"

If we then ask the player about their class:

PROMPT "Tell me your class:"

the class will jump on the top of the stack, pushing all the other values "down", and resulting in something like this:

%1 "Warrior"
%2 "John"

The thing to remember is that the return values go to the top of the stack, subsequently pushing the existing values "lower".

The values on the stack can be referred to in command arguments. So the command:

DISPLAY "Hello %2, mighty %1!"

will display the text Hello John, mighty Warrior!

The stack in GameLoops can be only pushed to, there is no way to revoke/pop values from it (although they can be retrieved like shown above).

Storing values

Values in GameLoops can also be stored in a single hierarchical storage organized like a tree. Since the values on the stack constantly move downward, the storage provides more predictable way to refer to the most important game data. There are basically two commands for using the storage: STORE and RETRIEVE. STORE puts a value in the tree:

PROMPT "Tell me your name:"
STORE "/player/name", "%1"
PROMPT "Tell me your class:"
STORE "/player/class", "%1"

The first argument above specifies a path (sequence of nodes) in the tree-like storage. So the player name is stored in the subnode "name" of the top-level node "player" and the player class in its subnode "class" in the storage. Both those values can be retrieved at any time to the top of the stack with the RETRIEVE command:

RETRIEVE "/player/name"
DISPLAY "Be greeted %1!"

The storage is hierarchical, so you can also retrieve the whole top-level node "/player":

RETRIEVE "/player"
DISPLAY "%1"

The result would be {name: "John", class: "Warrior"} (as the storage is basically a JSON tree).

Note that it is also perfectly valid to use parameters like %1 in the path, like in the example below:

PROMPT "Tell me your name:"
PROMPT "Tell me your class:"
STORE "/characters/%2/class", "%1"
...
PROMPT "Which character would you like to play?"
RETRIEVE "/characters/%1/class"
DISPLAY "Hello mighty %1!"