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• Characters
• ACL2-built-ins

Digit-char-p

The number, if any, corresponding to a given character

(digit-char-p ch) is the integer corresponding to the character ch in base 10. For example, (digit-char-p #\3) is equal to the integer 3. More generally, an optional second argument specifies the radix (default 10, as indicated above).

The guard for digit-char-p (more precisely, for the function our-digit-char-p that calls of this macro expand to) requires its second argument to be an integer between 2 and 36, inclusive, and its first argument to be a character.

Digit-char-p is a Common Lisp function, though it is implemented in the ACL2 logic as an ACL2 macro. See any Common Lisp documentation for more information.

Macro: digit-char-p

(defmacro digit-char-p (ch &optional (radix '10))
  (cons 'our-digit-char-p
        (cons ch (cons radix 'nil))))

Function: our-digit-char-p

(defun our-digit-char-p (ch radix)
  (declare (xargs :guard (and (characterp ch)
                              (integerp radix)
                              (<= 2 radix)
                              (<= radix 36))))
  (let ((l (assoc ch
                  '((#\0 . 0)
                    (#\1 . 1)
                    (#\2 . 2)
                    (#\3 . 3)
                    (#\4 . 4)
                    (#\5 . 5)
                    (#\6 . 6)
                    (#\7 . 7)
                    (#\8 . 8)
                    (#\9 . 9)
                    (#\a . 10)
                    (#\b . 11)
                    (#\c . 12)
                    (#\d . 13)
                    (#\e . 14)
                    (#\f . 15)
                    (#\g . 16)
                    (#\h . 17)
                    (#\i . 18)
                    (#\j . 19)
                    (#\k . 20)
                    (#\l . 21)
                    (#\m . 22)
                    (#\n . 23)
                    (#\o . 24)
                    (#\p . 25)
                    (#\q . 26)
                    (#\r . 27)
                    (#\s . 28)
                    (#\t . 29)
                    (#\u . 30)
                    (#\v . 31)
                    (#\w . 32)
                    (#\x . 33)
                    (#\y . 34)
                    (#\z . 35)
                    (#\A . 10)
                    (#\B . 11)
                    (#\C . 12)
                    (#\D . 13)
                    (#\E . 14)
                    (#\F . 15)
                    (#\G . 16)
                    (#\H . 17)
                    (#\I . 18)
                    (#\J . 19)
                    (#\K . 20)
                    (#\L . 21)
                    (#\M . 22)
                    (#\N . 23)
                    (#\O . 24)
                    (#\P . 25)
                    (#\Q . 26)
                    (#\R . 27)
                    (#\S . 28)
                    (#\T . 29)
                    (#\U . 30)
                    (#\V . 31)
                    (#\W . 32)
                    (#\X . 33)
                    (#\Y . 34)
                    (#\Z . 35)))))
    (cond ((and l (< (cdr l) radix)) (cdr l))
          (t nil))))