Angel \”Java\” Lopez on Blog

December 10, 2014

SimpleLisp (2) Compiling Lisp Values and Variables to JavaScript

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Let’s review the project’s implementation

https://github.com/ajlopez/SimpleLisp

the Lisp compiler to JavaScript, written in JavaScript, following the workflow of TDD (Test-Driven Development). All is “work in progress”, so today I will explain part of the implementation but it could be change in the future, when new use cases were added, and new ways of doing things were implemented.

I took the decision that each Lisp symbol is a JavaScript variable. So, the compilation of a symbol is:

exports['compile symbol'] = function (test) {
    test.equal(sl.compile('a'), 'a');
}

The sl is the SimpleLisp module, loaded in this test file (test/compile.js)

An integer and an string are compiled to natural values in JavaScript:

exports['compile integer'] = function (test) {
    test.equal(sl.compile('42'), '42');
}

exports['compile string'] = function (test) {
    test.equal(sl.compile('"foo"'), '"foo"');
}

It’s quoted values, too:

exports['compile quoted integer'] = function (test) {
    test.equal(sl.compile("'42"), '42');
}

exports['compile quoted string'] = function (test) {
    test.equal(sl.compile("'\"foo\""), '"foo"');
}

I decided to compile Lisp nil to JavaScript null. The boolean values are the same:

exports['compile nil'] = function (test) {
    test.equal(sl.compile('nil'), 'null');
}

exports['compile booleans'] = function (test) {
    test.strictEqual(sl.compile('false'), 'false');
    test.strictEqual(sl.compile('true'), 'true');
}

But, what happens if an expression serie is compiled? I build an anonymous function, invoked without arguments, and the last expression value is returned:

exports['compile two symbols'] = function (test) {
    test.equal(sl.compile('a b'), '(function () { a; return b; })()');
}

Next topics: compilation of a Lisp lisp, and more quoted values, macros, ect.

Stay tuned!

Angel “Java” Lopez

http://www.ajlopez.com

http://twitter.com/ajlopez

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