To Generate or not Generate That is The Question

Generating JSON

I wanted to develop a node editor for my branching story lines.

While developing a node editor for dialog trees I came to the problem of bridging the gap from creating dialog in a UI to actually using the created dialog in code.

The dialog tree has conditions for branching dialog, instructions that mutate the game state and the ability to dispatch events. Now my problem was how can I actually use this in my game?

My first instinct was generating data in form of JSON or maybe XML. Because I was using JavaScript for the editor and the game I thought JSON would be a good target. But soon a problem emerged. Because of the integrating of conditions and instructions that need to be evaluated, we needed a way to translate conditions to data.

But if we do that, we inevitably have to create an interpreter for that data.

This just felt wrong for what ever reason. I really wanted not data in form of JSON or XML. What I really wanted was a program.

Generating Code

Now we would generate source code and simply execute it. While executing arbitrary code is not safe. We can make it safe using sandbox techniques. I personally like what Figma has done by embedding QuickJS as a WASM module. I personally use QuickJS Sandbox to achieve the same thing.

Why?

Sending not only the dialog data but also the program that interprets it is a powerful concept. Alan Kay similarly described something in his talk The Computer Revolution Hasn’t Happened Yet (If you just want to read the passage see No Formats, no Format Wars).

Of course generating source code comes with its own hiccups, but its a trade-off I am ready to pay.