Writing conditional logic

If you've ever read an interactive fiction book, you might be familiar with how it works. At the end of the page, you're faced with a choice like:

"Now where do we go?", Evan asked.
"Pfft, you tell me," Naomi replied.

WHERE DO EVAN AND NAOMI GO?
Straight, into the clearing: turn to page 86
Left, toward the river: turn to page 110

Many wonderful stories have been told with simple pathing like this. But there's an important limitation to this approach: once you turn to a specific page, the book isn't—cannot be—aware of where you jumped from. It has no memory of the reader's choice.

That sounds trivial, but think about it: what if you could remember a choice at the beginning of the narrative, and use it to inform the ending? What if you could determine the direction of a plot arc not off of a single decision, but many of them at once?

Variables allow us to do that. A variable is nothing more than a little piece of memory that your project holds on to. You might have a variable that stores whether Evan and Naomi chose straightOrLeft, if they started their adventure inTheMorning, or whether they decided to ford the river or swim when they made their decision on that riverCrossing.

All of the pathing in Choicelab is built off of variables, and writing opportunities for players to make choices that set variables to create conditional logic.

Kinds of variables

Choicelab supports three kinds of variables:

• String: A piece of text, typically a word or short sentence.
• Boolean: A "binary" value that must always be either true or false.
• Number: A fixed number.

This list may expand over time—there are many more from the world of coding that may enable more intricate, complex logic—but you'll be surprised by what's possible with these three types alone.

Writing conditional logic in branches

As covered in the previous chapter, you can add a branch to your project flowchart to create paths, which are attached to one or more branch stems.

[image: branch stems]

Each stem contains at least one rule. A rule looks at the value of a variable that's stored in the project playback's memory—set by the player's choices while going through your project—and compares it against what you want the value to be.

[image: rule]

A single rule can only evaluate one variable: 1 rule, 1 variable. That said, a stem can specify more than one rule, and be set to validate if the player's variables match all of the stem's rules, or just any one of them.

This set of tools—branch stems that contain one or more rules, each of which checks a single variable—lets you create relatively complex conditional logic. But, you may be wondering: how do you make an input button set a variable?

Setting variables