ykskb / lips

Mini Lisp Interpreter in 300 lines of Lisp

lips

Mini Lisp in 300 lines of Lisp

This is a very minimal Lisp interpreter written in Lisp. I made it because I wanted to learn Lisp and I was also interested in a Lisp project setup with tools like Roswell and fiveam.

It's nowhere near a full-fledged Lisp, nor does it intend to be, yet I found it to be a good exercise to make some Lisp in Lisp to get myself familiarized with a bit of Lisp.

Supported Features

• nil, integers, symbols
• define (not ANSI CL)
• if
• +, -, /, * and =
• lambda
• user-defined functions
• lexically-scoped variables
• progn
• quote (data)
• back quote interpolation
• macro
• macroexpand

Examples of Supported Codes

• Recursive fibonacci function

(define fibonacci (lambda (n) (if (= n 0) nil (if (= n 1) 0 (if (= n 2) 1 (+ (fibonacci (- n 1)) (fibonacci (- n 2))))))))
(fibonacci 12)
; 89

• unless macro

(defmacro unless (cond body) `(if ,cond () ,body))
(macroexpand '(unless (= 3 4) 1))
; (if (= 3 4) NIL 1)
(unless (= 3 4) 1)
; 1

• Back quote interpolation & evaluation

(define n 3)
`,(+ 2 n)
; 5

How to Run

Clone the project under local-projects directory of Quicklisp or Roswell, and run commands as below.

Using Roswell

./roswell/lips.ros

Using Quicklisp

(ql:quickload '(:lips) :silent t)
(lips:lips)

Exit

(lips:exit)

Test

(ql:quickload :fiveam)
(load #p"lips.asd")
(load #p"lips-test.asd")
(asdf:test-system :lips)