Arrow Navigation

By the end of this guide, you will:

• Add a selected field to your Model to track which file is highlighted

• Use model.with(...) to create updated state immutably

• Use case message in type: :key, code: to match keyboard events

• Use | alternation to match multiple keys in one pattern ("down" | "j")

• Use modifiers: to match modifier keys (e.g., modifiers: ["shift"] for Shift+G)

• Handle arrow keys (up/down) and vim keys (j/k) in one Update

• Return an updated model from Update to change state

• Write tests that verify state transitions (selected_index: 0 → 1)

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User Stories

Story -1: Arrow Key Navigation

As a terminal user
I want to navigate through the file list with arrow keys
So that I can select different files

Acceptance Criteria

• Up/Down arrow keys change which file is highlighted

• ‘j’/‘k’ vim keys also work for navigation

• Selection wraps at top/bottom of list

• Visual highlight follows selection

Notes

• Still using hardcoded file list

• Adds interactive navigation

Previous: Static File List | Next: Real Files