adrianton3 / espace

S-expression parser and macro expander

espace

S-expression parser in JavaScript

• Tokens
• Tree
• Macros

Tokenizer

const options = { 
    whitespace: false,
    comments: false,
    coords: true,
    prefixes: {
        '#': 'map',
    },
}

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

Parser

const source = '(fun (a b) (+ a b))'
const tokens = espace.Tokenizer.tokenize(source)
const tree = espace.Parser.parse(tokens) //

Macro expander

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

const parse = (source) => 
    espace.Parser.parse(espace.Tokenizer.tokenize(source))

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

espace.Expander.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))