simple s-expression parser for typescript

s-expression.ts

export function parse(lisp: string) {
    const lexer = /"[^"]*"|\(|\)|[^\s()]+/g;
    const ts = lisp.match(lexer)!;
    let i = 0
    const rec = () => {
        let prg: any = undefined
        while (i < ts.length) {
            if (ts[i] === '(') {
                if (!prg) {
                    prg = []
                } else {
                    prg.push(rec())
                }
            } else if (ts[i] === ')') {
                return prg
            } else {
                prg.push(ts[i])
            }
            i++
        }
        return prg
    }
    return rec()
}

test.ts

const test = `
(progn
    (dropempty query)
    (keys result)
    (drop result ('id 'access))
    (first result)
    (if (ne result 'status)
        (return 'Error "You cannot update this" 401)
        (else (return 'Success)))
`
console.log(JSON.stringify(parse(test)))