scm-slang

scm-slang?

scm-slang is an experimental implementation of the Scheme programming language designed for compatibiity with the online learning environment of Source Academy. It aims to be faithful to the original Structure and Interpretation of Computer Programs (SICP) book whilst maintaining compatibility with modules designed for use with js-slang, a subset of JavaScript intended for use with the SICP JS book in Source Academy.

scm-slang provides a special Scheme parser that is able to parse Scheme code. It also supports standard Scheme data structures such as Lists, Vectors and the Numeric tower.

How does it work?

scm-slang parses a subset of Scheme (minimally, enough to fulfil SICP chapters 1-4) and generates an estree-compatible AST. This way, scm-slang allows code written in SCM Source Languages to use modules written for JS Source Languages.

Comparison with Revised⁷ Report on the Algorithmic Language Scheme

scm-slang ultimately follows the R7RS language specification of Scheme. However, there are several key deviations that differentiate scm-slang from a complete implementation of R7RS Scheme:

• Continuations: The parser itself does not support continuations, but in conjunction with the Source Academy Explicit Control Evaluator, continuations are supported within the Source Academy ecosystem.

• Macros: Not implemented at the moment. Set for completion in Autumn-Fall 2024.

• Types: scm-slang does not support characters or bytevectors at the moment.

• Parentheses: scm-slang supports the use of square brackets (i.e. []) interchangably with parentheses in order to enhance the visual representation of Scheme code, similar to Racket or Guile Scheme. See relevant discussion here

• Named let is not supported.

• Import/Export: scm-slang follows a specialised import/export system that deviates from any standard Scheme implementation. It follows more closely to JavaScript syntax so as to maintain compatibility with current Source Academy modules.

;equivalent JavaScript to import:
;import { stack, beside } from "runes";
(import "runes" (stack beside))

;equivalent JavaScript to export:
;export let foo = "bar";
(export (define foo "bar"))

Requirements

• node: known working version: v20.11.0

Usage

To build,

$ git clone https://github.com/source-academy/scm-slang.git
$ cd scm-slang
$ yarn