This project is an implementation of the Scheme programming language written in pure version 1.5 Javascript. The original intent was to create a completely portable, platform-agnostic Scheme implementation, capable of running all of the examples from the book The Little Schemer.
It works by first parsing the input code into a hierarical structure of Atom and List objects, and then evaluating the structure from the outside in.
Global variables are supported, as are localized variables using let and let*. These forms introduce Scope objects, which are passed down the hierarchy and attached to atoms and lists for their evaluation.
Lambdas are also supported, and some recursive forms are achievable. Bearing in mind that each interpreted function call may represent more than one call in Javascript, the recursive addition function defined as:
(define add
(lambda (x y)
(if (= y 0) x
(+ 1 (add x (- y 1))))))will add values up to 1315 in Google Chrome. Some more complex recursive functions will fail due to a bug that I have yet to track down. An example is the Fibonacci function defined as:
(define fib
(lambda (i)
(if (< i 2) i
(+ (fib (- i 1))
(fib (- i 2))))))Point your browser at file:///path/to/project/content/scheme.htm. Tests will run automatically, click the ‘Display Test Results’ button to see the results from all unit and integration tests.
Code in the textarea can be executed either by clicking the ‘Execute’ button or pressing Enter when the textarea is in focus.
Tests can also be run from the command line using the Rake task ‘test:rhino’. Mozilla Rhino must be installed and available from the current $PATH. Node.js support is underway, but not working yet.
The integration test script “littleSchemerTest.js” contains implementations of the examples in the Little Schemer, to ensure that those examples actually work in this implementation. It is highly recommended that you not open this file directly if you’re working through the book.