embedded numbers sum

Write a function accepting a string and returning the sum of the numbers contained in the string.

 $ cat ens.rkt 
 #lang racket 
  
 (define (ens s) 
  
   ; Return the sum of the numbers found in the given string. 
  
    
   (define char->number 
     (let ((c2n #hasheq((#\0 . 0) (#\1 . 1) (#\2 . 2) (#\3 . 3) (#\4 . 4)  
                        (#\5 . 5) (#\6 . 6) (#\7 . 7) (#\8 . 8) (#\9 . 9)))) 
       (lambda (c) (hash-ref c2n c)))) 
  
  
   (define (parse-number chars sum n) 
     (if (null? chars) 
       (+ sum n) 
       (let ((char (car chars)) 
             (chars (cdr chars))) 
         (if (char-numeric? char) 
           (parse-number chars sum (+ (* n 10) (char->number char))) 
           (parse-letters chars (+ sum n)))))) 
  
  
   (define (parse-letters chars sum) 
     (if (null? chars) 
       sum 
       (let ((char (car chars)) 
            (chars (cdr chars))) 
         (if (char-numeric? char) 
           (parse-number chars sum (char->number char)) 
           (parse-letters chars sum))))) 
  
  
   (parse-letters (string->list s) 0)) 
  
  
 (require rackunit) 
  
 (check-eq? (ens "") 0) 
 (check-eq? (ens "11aa22bb33cc44") 110) 
 (check-eq? 
   (ens "Annual income 20 pounds, annual expenditure 19 19 and 6, result happiness") 
   64) 
  
 $ racket ens.rkt 
  
 $