cis352-s26

Lambda Calculus Explorer

An interactive web application for exploring the untyped lambda calculus. Built for CIS352 at Syracuse University.

Enter lambda terms, click subterms to reduce them, and explore different reduction paths through a branching derivation tree.

Features

• Interactive reduction: click any redex and choose beta, alpha, or eta
• Four reduction strategies: Normal, Applicative, Call-by-Value, Call-by-Name
• Derivation tree: visual DAG of all reduction paths, with branch/merge tracking
• Self-loop detection: dashed arrow when a term (like omega) reduces to itself
• Binding arrows: hover a variable to see an arrow to its binder
• 15-slide interactive tutorial: learn lambda calculus step by step
• 40+ built-in examples: combinators, Church numerals, Booleans, lists, recursion
• URL deep-linking: share terms via ?term=... parameter
• Keyboard-driven: Space to step, B to reveal redexes, arrow keys to navigate

Prerequisites

• Rust (stable)
• wasm-pack
• Node.js (v18+)

Build & Run

npm install
./build.sh                # builds WASM + TypeScript
cd www && python3 -m http.server 8080
# open http://localhost:8080

For development with auto-rebuild:

npm run watch             # recompiles TypeScript on save

Architecture

Layer	Tech	Source
Core logic	Rust -> WASM	src/ (term, parser, render, WASM API)
Frontend	TypeScript (strict)	www/src/app.ts, www/src/types.ts
Bundler	esbuild	esbuild.mjs
Styles	CSS (custom properties)	www/style.css

109 Rust tests (cargo test). TypeScript type-checks with npm run check.

Building Lectures

The tutorial system supports custom interactive slide decks. Add slides to the TUTORIAL_STEPS array in www/src/app.ts – each slide can load a term, auto-step, demo strategies, or run convergence proofs.

See docs/TUTORIAL_AUTHORING.md for the full authoring guide.

Syntax

variable:     x, y, foo
abstraction:  (λ (x) body)        -- also \ or lambda
application:  (e1 e2)
multi-param:  (λ (x y z) body)    -- curried sugar
multi-app:    (f a b c)           -- left-associative sugar

License

ISC