scheme

A toy Scheme interpreter implemented with JavaScript ES6.
Browser REPL: https://shuding.github.io/scheme

Usage

NodeJS >= 6

Run test: node test/test.js
Run repl: node src/repl.js

REPL demo

Basic, define, functions

2                                   ; -> 2
"hello, world"                      ; -> hello, world
true                                ; -> true
(+ 1 (* 2 (- 3 (/ 4 2))))           ; -> 3

(define the_answer 42)
the_answer                          ; -> 42

(define (square x)
        (* x x))
(square (square 3))                 ; -> 81

(define (not x)
        (cond (x false)
              (true true)))
(not true)                          ; -> false

Recursive

(define (if x a b)
        (cond (x a)
              (true b)))

(define (fact n)
        (if (= 0 n)
            1
            (* n (fact (- n 1)))))

(fact 5)                            ; -> 120

List

(define (length x)
        (cond ((= null (car x)) 0)
              (true (+ 1 (length (cdr x))))))
(length (list 1 2 3))                        ; -> 3

Filter

(define (filter x y)
        (cond ((= null (car x)) (list))
              ((y (car x)) (prepend (car x) (filter (cdr x) y)))
              (true (filter (cdr x) y))))

(define (greater_than_one x)
        (> x 1))

(filter (list 1 2 3 4 5) greater_than_one)   ; -> 2,3,4,5,

Index

(define (index x i)
        (cond ((= i 0) (car x))
              (true (index (cdr x) (- i 1)))))
(index (list 1 2 3) 2)                       ; -> 3

Lambda

((lambda x (+ x 1)) 3)             ; -> 4

(define (add_x_fn x) (lambda y (+ x y)))
(define add_10_fn (add_x_fn 10))
(add_10_fn 1)                      ; -> 11

JS lib

const { Scope, rootScope } = require('./src/default')

let t = new Scope({}, rootScope)

t.eval(`(+ 1 (* 2 (- 3 (/ 4 2))))`)

Immutable (inhertance)

const { Scope, rootScope } = require('./src/default')

let t = new Scope({}, rootScope), p

t = t.eval(`(define test 1)`)
p = t.eval(`(define test 2)`)

t.eval(`test`) // => 1
p.eval(`test`) // => 2

Defaults

const { Scope, rootScope } = require('./src/default')
let t = new Scope({ x: 2 }, rootScope)

t.eval(`(+ x 1)`) // => 3

Acknowledgement

No dependencies, built for learning SICP & writing exercises in the book.

License

MIT License

Copyright (c) 2016 Shu Ding

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.