#include "stdlib.lisp"

(define str-elem (ch str)
    (if (= str "") 0
        (if (= ch (substr 0 1 str)) 1
            (str-elem ch (substr 1 -1 str)))))

(define isspace? (ch)
    (str-elem ch " \n\t\r"))

(define isdigit? (ch)
    (let ((n (ord ch))) (and (<= 48 n) (<= 57 n))))

(define lowercase? (ch)
    (let ((n (ord ch))) (and (<= 97 n) (<= n 122))))

(define uppercase? (ch)
    (let ((n (ord ch))) (and (<= 65 n) (<= n 90))))

(define iswordchar? (ch)
    (or (str-elem ch "-_?")
        (or (lowercase? ch) (uppercase? ch))))

(define isrestwordchar? (ch)
    (or (iswordchar? ch) (isdigit? ch)))

(define parse-int (str)
    (let ((helper (lambdarec rec (str n)
                        (let ((ch (substr 0 1 str))
                              (rest (substr 1 -1 str)))
                            (if (isdigit? ch)
                                (rec rest (+ (* 10 n) (- (ord ch) 48)))
                                n)))))
        (helper str 0)))

(define next-token (str)
    (let ((ch (substr 0 1 str))
          (rest (substr 1 -1 str)))
        (cond
            (= ch "")
                '()
            (isspace? ch)
                (next-token rest)
            (= ch ";")
                (next-token (drop-while (lambda (c) (not (= c "\n"))) rest))
            (= ch "(")
                (list "(" rest)
            (= ch ")")
                (list ")" rest)
            (iswordchar? ch)
                (let ((restword (take-while isrestwordchar? rest)))
                    (list (concat ch restword) (substr (length restword) -1 rest)))
            (isdigit? ch)
                (let ((word (concat ch (take-while isdigit? rest))))
                    (list (parse-int word) (substr (length word) -1 str)))
            (do
                (print (concat "Invalid token: " ch))
                (exit)))))

; (define parse-sexpr (tokens)
;     ...)