(module xref racket
  
  (define (get-lines file)
    (call-with-input-file file
      (lambda (in)
        (let loop ([str (read-line in)])
          (if (eof-object? str) 
              empty
              (cons str (loop (read-line in))))))))
  
  
  (define (parse stx)
    
    (syntax-case stx ()
      [id (identifier? #'id) (cons #'id empty)]
      [(e1 e2 ...) (apply append (map parse (syntax->list #'(e1 e2 ...))))]
      [else empty]))

  (define (pos->line lines pos)    
    (define (check-lines lines current-pos)     
      (cond
        [(empty? lines) (error 'oops)]
        [(<= pos (+ current-pos (string-length (first lines)))) 1]
        [else (+ 1 (check-lines (rest lines) (+ current-pos 1 (string-length (first lines)))))]))    
    (check-lines lines 0))
    
  
  (define (get-refs file)
    
    (define lines (get-lines file))
    
    (call-with-input-file file
      (lambda (in)       
        (let ([ids (parse (read-syntax file in))])
          (let ([hash (make-hash)])
            (for-each
             (lambda (id)
               (with-syntax ([idc id])
                 (let ([sym (syntax->datum #''idc)]
                       [line (pos->line lines (syntax-position id))])
                   (hash-set! hash sym (cons line (hash-ref hash sym empty))))))
             ids)
            (hash-map hash cons))))))
  
  (get-refs "xref.rkt")
  
  
  )

;;sample run :

;'(('pos 23 19)
;  ('hash-ref 41)
;  ('<= 23)
;  ('empty? 22)
;  ('parse 34 16 12)
;  ('current-pos 24 23 20)
;  ('id 40 38 37 15 15 15)
;  ('get-lines 30 3)
;  ('with-syntax 38)
;  ('e2 16 16)
;  ('syntax->list 16)
;  ('let 39 35 34 6)
;  ('first 24 23)
;  ('syntax 39 16 15 15)
;  ('sym 41 41 39)
;  ('quote 39 22)
;  ('cond 21)
;  ('lambda 37 33 5)
;  ('read-line 9 6)
;  ('in 34 33 9 6 5)
;  ('e1 16 16)
;  ('for-each 36)
;  ('stx 14 12)
;  ('... 16 16)
;  ('define 30 28 20 19 12 3)
;  ('read-syntax 34)
;  ('append 16)
;  ('idc 39 38)
;  ('if 7)
;  ('rest 24)
;  ('+ 24 24 23)
;  ('map 16)
;  ('file 34 32 30 28 4 3)
;  ('identifier? 15)
;  ('hash-set! 41)
;  ('pos->line 40 19)
;  ('syntax-case 14)
;  ('string-length 24 23)
;  ('hash-map 43)
;  ('module 1)
;  ('str 9 7 6)
;  ('lines 40 30 25 24 24 23 22 20 19)
;  ('line 41 40)
;  ('make-hash 35)
;  ('syntax-position 40)
;  ('racket 1)
;  ('hash 43 41 41 35)
;  ('get-refs 45 28)
;  ('oops 22)
;  ('eof-object? 7)
;  ('apply 16)
;  ('call-with-input-file 32 4)
;  ('loop 9 6)
;  ('else 24 17)
;  ('syntax->datum 39)
;  ('cons 43 41 15 9)
;  ('empty 41 17 15 8)
;  ('error 22)
;  ('xref 1)
;  ('check-lines 25 24 20)
;  ('ids 42 34))