natural

Conformance: SketchyLISP Core

Purpose: Convert an integer or natural number to a natural number. Only non-negative integers can be converted to natural.

Arguments:
A - number

Implementation:

(define (natural x)
  (letrec
    ((_natural
       (lambda (list-x)
         (cond ((eq? (car list-x) '+) (cdr list-x))
           ((eq? (car list-x) '-)
             (bottom (list 'natural x)))
           (else list-x)))))
    (list->integer (_natural (integer->list x)) #t)))

Example:

(natural +123) 
=> 123

See also:
digits, integer, natural?.