; 1-800-ppraxis
 
(define (telemap c)
  (case (char-upcase c)
    ((#\A #\B #\C)     #\2)
    ((#\D #\E #\F)     #\3)
    ((#\G #\H #\I)     #\4)
    ((#\J #\K #\L)     #\5)
    ((#\M #\N #\O)     #\6)
    ((#\P #\Q #\R #\S) #\7)
    ((#\T #\U #\V)     #\8)
    ((#\W #\X #\Y #\Z) #\9)
    (else c)))
 
(define (telemapper str)
  (list->string
    (filter char-numeric?
      (map telemap
        (string->list str)))))
 
(display (telemapper "1-800-PPRAXIS")) (newline)

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