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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))))