12. Functions

Eleven sessions. Eleven games. One game waiting in the backlog since day one. She didn’t ask about the Sherlock Holmes game at the end of this session. She didn’t need to. She was already there.

A set of steps with a name

A function is a set of steps bundled together and given a name. Instead of writing or saying the same sequence of instructions every time, you write it once, name it, and call the name whenever you need it.

I started with her skin routine. Every morning, same steps, same order. She doesn’t think through each step individually. She runs the routine. The routine is the function.

Then I told her about the house cleaning checklist I’d made. Clean kitchen doesn’t mean one thing — it means wipe the counters, clean the stove, empty the bin, wash the dishes, mop the floor, put things back in their places. Fifteen tasks. But I don’t recite all fifteen every time. I say clean kitchen and everyone knows what that means.

And then the dessert we’d invented together. Hung curd, chopped fruit, a specific way of mixing it. We’d named it Bu Yum. Now when anyone in the house says Bu Yum, the whole recipe is implied. The name carries the function.

She understood it immediately. But understanding a concept and knowing how to build a game around it are different things. And this was the session where that gap showed up first.

How she chose what to build

Her first attempt was a game called Name the Game.

She’d understood that functions bundle steps and give them a name — so she designed a game where the player names what a stick figure is doing based on its actions.

A stick figure turns around, waves, wriggles, and sits down. Is it in dance class? Trying to make a baby laugh? Signalling for help?

A stick figure picks up a teapot, pours tea, sips it, then dances happily. Did it get a caffeine rush? Is it teaching someone to dance? Trying to make a baby laugh?

The idea was there. The stick figure’s actions were the steps. The player had to name the function — identify what bundle of actions added up to.

But the game wasn’t performing any functions. It was describing them. The player was recognising named actions, not calling a function and watching it execute.

I told her. She understood the difference but got stuck on how to build a game where a function actually ran — where you called a name and something happened as a result.

I gave her the dance example. Imagine four moves: jump, wave, spin, cartwheel. Those are the steps. Now bundle them in different orders and name each combination. Silly Dance: wave, spin, wave. Athletic Dance: jump, cartwheel, jump. Party Dance: spin, wave, cartwheel, spin. Each name calls a specific sequence. Each sequence produces a different performance.

She sat with that for a moment.

Then she mentioned Joy.

She and her best friend Joy have a game they play — they reverse each other’s names as a kind of code language. YOJ and IBUS. They have been playing scrabble together for few years. A reversal is a function. Input goes in. The reversal rule is applied. Output comes out. Every time.

The Secret Spy game arrived fully formed almost immediately after that.

The design doc

The Secret Spy

Mission: Find the code which three friends are using in order to spy on their messages.

Instance 1: Find the code that the three friends have used.
Coded message: WORROMOT TUOEDIH EHT TA EM TEEM
Uncoded message: MEET ME AT THE HIDEOUT TOMORROW

Options:
- It reverses the letters and words in order to form a sentence
- It reverses only some letters while in the others it is normal
- It reverses all the letters but not the words

Answer: It reverses the letters and words in order to form a sentence

Instance 2: Find the code that the friends have used.
Coded message: THE DROWSSAP IS EEW YLLIW AKNOW. REMEMBER SYUG. THE TUOEDIH IS NO THE DNOCES TREE OT ETH RIGHT.
Uncoded message: THE HIDEOUT IS ON THE SECOND TREE TO THE RIGHT. THE PASSWORD IS WEE WILLY WONKA. REMEMBER GUYS.

Options:
- It reverses the letters alternatively and reverses the sentences instead of the words
- It reverses only some letters while in the others it is normal
- It takes the first letter, puts it at the last and the rest stays the same

Answer: It reverses the letters alternatively and reverses the sentences instead of the words

Instance 3: Find the code that the friends have used.
Coded message: AKEM URES OT EEPK HOSET MALLS IDSK UTO FO URO USINESSB
Uncoded message: MAKE SURE TO KEEP THOSE SMALL KIDS OUT OF OUR BUSINESS

Options:

- It reverses only some letters while in the others it is normal
- It reverses the letters alternatively and reverses the sentences instead of the words
- It takes the first letter, puts it at the last and the rest stays the same

Answer: It takes the first letter, puts it at the last and the rest stays the same

Instructions for ChatGPT: Single HTML file. Black background, white font and buttons. Title "The Secret Spy" at top centre. Mission written below title. Instances written as MCQ questions below mission. Options are clickable. Wrong answer — Game Over with Play Again button. Play Again restarts game. All correct — You Won with Play Again button. Mobile screen design. Answers for ChatGPT reference only.

Each instance uses a different cipher — a different function. Same input format — a coded message — but a different transformation rule applied each time. The player’s job is to identify the function from its output. Work backwards from what came out to understand the rule that produced it.

That’s a sophisticated game design decision. She’s not asking the player to apply a function. She’s asking the player to reverse-engineer one.

And the password in Instance 2:WEE WILLY WONKA: is pure nine-year-old. Some things don’t need explaining.

Design → Build → Ship

Clean build. The concept was clear, the game idea was precise, and the design doc reflected both.

She’d been building under the constraint for six sessions now. The brief was tight. The output matched.

No significant bugs. No tears. No twelve-prompt debugging sessions. A session that moved as quickly as the concept had landed — which was quickly, once Joy and the reversed names unlocked it.

What this is actually building

The maths question is the thing I keep coming back to.

She asked it before building anything. Before the stick figure attempt, before the Name the Game confusion, before Joy and the spy game arrived. She sat with the concept for a few minutes and asked: is this the same as what I already know?

That’s the instinct of someone who has learned to look for connections before accepting that something is entirely new. Eleven sessions of naming concepts that were already present in her experience had built a habit: when you encounter something new, ask first whether it’s actually new or whether it’s something familiar seen from a different angle.

The answer, in this case, was mostly the same thing but bigger. She accepted that and moved on.

The stick figure attempt matters too — not because it worked but because it showed exactly where the gap was. She understood the concept. She couldn’t yet translate it into a game mechanic. That gap — between understanding and building — is real and it’s different from not understanding. The dance example closed it. Joy closed the rest.

Functions is where she learned that the best designs come from problems you’ve already lived — and that a childhood code language with a best friend is a function you’ve been calling for years without knowing the name.

Functions is where she knew it was almost over. And she was ready. ⚡️

What’s next

She knew this was the last concept before the free build.

Eleven sessions. Eleven games. And one game that had been waiting in the backlog since day one.

She didn’t ask about the Sherlock Holmes game at the end of this session. She didn’t need to. She was already there.

New here? Start with the series introduction. Parent’s Guide: Computational Thinking for Pre-Teens