Source (programming language)


Source is a family of sublanguages of JavaScript, developed for the textbook Structure and Interpretation of Computer Programs, JavaScript Adaptation. The JavaScript sublanguages Source §1, Source §2, Source §3 and Source §4 are designed to be just powerful enough to support all examples of the respective chapter of the textbook.

Purpose and design principle

During the development of SICP JS, starting in 2008, it became clear that purpose-designed sublanguages of JavaScript would contribute to the learning experience. Initially called "JediScript" and inspired by, Douglas Crockford, the Source sublanguages follow the chapters of SICP JS; each language Source §x is a sublanguage of the next language Source §.

Features

Source §1 is a very small purely functional sublanguage of JavaScript, designed for Chapter 1 of SICP JS. Source §2 adds pairs and a list library, following the data structures theme of Chapter 2. Source §3 adds state-full constructs, and Source §4 adds support for meta-circular evaluation. Chapter 5 of SICP JS does not require language support beyond Source §4. All Source languages are properly tail recursive, as required by Chapter 1 of SICP and as specified by ECMAScript 2016.

Implementations

Since the Safari browser is ECMAScript 2016 compliant, including proper tail calls, it can serve as an implementation of all Source languages, provided that the necessary libraries are loaded. The Source Academy is a web-based programming environment that implements all Source languages, regardless of browser support for proper tail calls, and features various tools for the readers of SICP JS. The language implementation in the Source Academy is an open-source project.