#lang plait
(define (digit-num n)
(cond [(<= n 9) (some 1)]
[(<= n 99) (some 2)]
[(<= n 999) (some 3)]
[else (none)]))
#lang plait
(define (digit-num n)
(cond [(<= n 9) (some 1)]
[(<= n 99) (some 2)]
[(<= n 999) (some 3)]
[else (none)]))