# Microtables - LLM Navigation Guide

## Project Overview
A lightweight spreadsheet application positioned between a calculator and a full office suite — fast loading, common spreadsheet operations.

## Architecture
- `/frontend/` - ClojureScript (Reagent + re-frame, shadow-cljs). Fully functional standalone.
- `/server/` - Express, minimal; will eventually handle persistence and collaboration.

## Key Concepts

### Data Structure
The spreadsheet data is a nested map: `{column-letter {row-number {:value ...}}}`

Example:
```clojure
{"A" {1 {:value 78 :inbound [...]}
      3 {:value "=B2 * 4" :refs [...]}}
 "B" {2 {:value "=A1 + 3" :refs [...] :inbound [...]}}}
```

### Formula System
- Formulae start with `=` and are evaluated using **math.js** library
- Range syntax supported: `=sum(A1:A10)`
- Cell references create a **doubly-linked tree structure**:
  - `:refs` - forward references (cells this formula depends on)
  - `:inbound` - back references (cells that depend on this cell)
  - `:display` - computed/evaluated value shown to user
  - `:value` - raw user input
  - `:dirty` - flag indicating re-evaluation needed

### Evaluation Flow
A cell change re-parses references, updates `:refs`/`:inbound`, evaluates the cell, then recursively evaluates its `:inbound` queue (cycle detection prevents infinite loops).

## Development Notes
- `todo.md` has a running list of desired changes
- Data structures prioritize clarity over micro-optimization (small dataset assumption)

## Common Tasks
- **Install an npm dependency**: add it to `shadow-cljs.edn` (not just `package.json`), then restart the dev server