tysp

An interpreter for a simple Scheme (dialect of Lisp), written in Typescript. Heavily inspired by Peter Norvig's guide to creating a Scheme interpreter in Python.

Why?

• Learn about the basics of PL design (e.g., What is an interpreter? How is syntax evaluated?)
• Get better at programming in Typescript
• Explore functional programming (again - perhaps I'll include features from Racket in future updates, as seen in CS135)

Overview

The interpreter is comprised of 2 main components:

• Parser - Tokenizing and Abstract Syntax Tree generation
• Evaluator - Perform desired operations based on an environment and scheme specific keywords (e.g., if, lambda, define)

The main features of this interpreter include:

• Mathematical and comparison operators
• Variable declarations
• Conditionals (if statements)
• Anonymous functions (e.g., Lambda functions)
• REPL for in-line evaluation

Setup

git clone https://github.com/kris-gaudel/tysp

Usage

To start the interpreter and its REPL, enter the directory and run :

npm start

Examples

tysp.ts> (expt 4 2)
16
tysp.ts> (define r 10)
undefined
tysp.ts> (* pi (* r r))
314.159265359
tysp.ts> (if (> (* 11 11) 120) (* 7 6) oops)
42
tysp.ts> (define fact (lambda (n) (if (<= n 1) 1 (* n (fact (- n 1))))))
undefined
tysp.ts> (fact 10)
362880

Next Steps

• Implement more functions (e.g., cons, eq?, etc)
• Testing