espace

S-expression parser in JavaScript

• Parser demo
• Macros demo

Tokenizer

const options = { 
    coords: true,
    prefixes: {
        '#': 'map',
        ':': 'key',
    },
}

const source = '(fun (a b) (+ a b))'
const tokens = tokenize(source, options) //

Parser

const source = '(fun (a b) (+ a b))'
const tree = parse(tokenize(source)) //

Macro expander

const source = '(+ a b c)'
const pattern = '(+ x y z)'
const replace = '(+ (+ x y) z)'

const getTree = (source) => parse(tokenize(source))

const sourceTree = getTree(source)
const patternTree = getTree(pattern)
const replaceTree = getTree(replace)

expand(sourceTree, patternTree, replaceTree) //

Pattern can have more than one level:

• can replace all subexpressions of the form (- (- x y)) with (- y x)

Pattern supports rest variables:

• can replace all (first (list x y...)) with (list y...)
• can replace all (last (list x... y)) with (list x...)

Variables prefixed by _ in replace get uniquely named:

• can replace all (swap x y) with (let (_tmp x) (set! x y) (set! y _tmp))