parsing lisp in lisp

plisp

#lang racket

(define (token)
  (let [(c (read-char))]
    ;(printf "DEBUG: ~s~%" c)
     c))

(define (whitespace? ch)
  (case ch
    ((#\space #\tab #\newline #\return)  #t)
    (else #f)))

(define (char? ch)
  (and (>= (char->integer ch) (char->integer #\a))
       (<= (char->integer ch) (char->integer #\z))))

(define (lambda? ch) (equal? #\λ ch))
(define (dot? ch) (equal? #\. ch))
(define (lparens? ch) (equal? #\( ch))
(define (rparens? ch) (equal? #\) ch))

(define (intern obj)
  (printf "INTERN: ~s~%" obj)
  obj)

(define readatom
  (lambda (ch)
    (cond
      ((whitespace? ch)  (readatom (token)))
      ((eof-object? ch)  null)
      ((lparens? ch)     (readlist (token)))
      (else (intern ch)))))

(define readlist
  (lambda (ch)
    (cond
      ((rparens? ch) null)
      ((whitespace? ch)  (readlist (token)))
      ((eof-object? ch)  null)
      (else (cons (readatom ch) (readlist (token)))))))

(printf "~s~%" (readatom (token)))