Architecture

Quantus is a Rust engine and a Tauri desktop app around it. The app calls the engine directly through Tauri commands: no server, no child process.

desktop/src/  (React, MathLive)
   │  invoke('evaluate', …)             desktop/src/api.ts
   ▼
desktop/src-tauri/  (Tauri commands)    commands.rs: lock the SessionStore, call the API
   │
   ▼
crates/quantus-core/src/api.rs          JSON request and response types
   │
   ├─ session.rs   session variables
   ├─ latex/       lexer → parser → AST → serializer
   ├─ eval/        evaluation, substitution, solver, derivatives
   ├─ algebra/     simplifying, factoring, the working
   ├─ analysis/    curve sketch, plot, tangent, area, table
   ├─ electro/     circuits: materials, wires, solver
   └─ num.rs, quantity.rs, units/   numbers, PhysicalQuantity, units

The workspace

Crate	Path	What it is
quantus-core	crates/quantus-core/	The engine, a library with no UI and no I/O
quantus-desktop	desktop/src-tauri/	The Tauri shell: commands, menu, single instance, settings file, bundling

The renderer in desktop/src/ is a React app built with Vite. It is not a crate; the Tauri build bundles it.

The engine

Module	Responsibility
num.rs	Value: exact rationals, $\pi$, $e$, roots and $i$; decimals with dashu and astro-float
quantity.rs	PhysicalQuantity: a value with a unit
units/	the unit table, prefixes, dimensions, conversion, named units and quantity names
latex/	lexer, parser, AST, normalizer and serializer for LaTeX in and out
eval/	evaluating the AST, substitution of session variables, the equation solver, symbolic derivatives, the step list of the calculator
algebra/	the simplification pipeline: expand, factor, combine, cancel, radicals, logs, trig identities, with a step per rule and the domain conditions
analysis/	Analysis mode: its own expression tree, derivatives with rules, domains, limits, antiderivatives, equation solving, the plot sampler and the tasks, all under a time budget
electro/	Electronics mode (not in the app yet): material table, wire resistance, the exact MNA solver, Newton iteration for power loads, reverse solving
settings.rs	Settings and Mode
session.rs	Session (the variables of one session) and SessionStore
text.rs	the language of texts the engine writes itself (msg!, Scope)
api.rs	the request and response types and one function per command

Dependencies point one way: numbers ← quantities ← units ← LaTeX I/O ← evaluation. The Tauri commands know nothing but api and SessionStore.

Principles

• Exact first. Arithmetic stays exact (rationals, symbolic $\pi$ and roots) until the result is written; decimals appear only at the output boundary.
• Nothing is guessed. Missing input is an error or an Unknown with a reason, never a silent default.
• The working is output. Steps are produced by the same code that does the work, not reconstructed afterwards.
• Stateless commands. The analysis and circuit commands take everything in the request; only evaluate and the variable commands touch the session.

Design documents

The specifications behind the larger features are kept in design/ in the repository, outside this site: the original specification (German), the analysis and electronics modes, the step detail levels and the release preparation.