---
id: LSN-0012
ticket: legacy-runtime-learn-import
title: Input Mental Model
created: 2026-03-27
tags: [migration, tech-debt]
---

# Input Mental Model

Status: pedagogical
Companion spec: [`../specs/06-input-peripheral.md`](../../specs/06-input-peripheral.md)

PROMETEU treats input as sampled state, not as an asynchronous event.

## State Versus Event

The most important model to understand is:

- a button does not "fire" an action by itself;
- a button changes state;
- the game reads that state during the frame.

That looks much more like classic console register polling than like modern UI callbacks.

## Why This Matters

This model:

- improves determinism;
- simplifies replay;
- makes debugging easier;
- makes the frame loop easier to read.

It also fits PROMETEU's identity better as a machine strongly inspired by retro hardware and DIY construction.

## Good Habits

- read input in `UPDATE`;
- map actions, not physical keys;
- separate input reading from heavy logic;
- treat polling as part of the frame budget.

## Teaching Value

The input peripheral helps teach:

- the difference between state and event;
- temporal sampling;
- synchronization between input and logic;
- determinism in interactive systems.