		Search-engine friendly clone of the ACL2 documentation.

Character-kinds

Letter-char-p

Recognize ASCII letters.

The built-in alpha-char-p has a guard requiring characters. In contrast, this recognizer has guard t.

Definitions and Theorems

Function: letter-char-p

(defun letter-char-p (x)
  (declare (xargs :guard t))
  (and (characterp x)
       (b* ((code (char-code x)))
         (or (and (<= (char-code #\A) code)
                  (<= code (char-code #\Z)))
             (and (<= (char-code #\a) code)
                  (<= code (char-code #\z)))))))

Theorem: booleanp-of-letter-char-p

(defthm booleanp-of-letter-char-p
  (booleanp (letter-char-p x))
  :rule-classes :type-prescription)

Theorem: characterp-when-letter-char-p

(defthm characterp-when-letter-char-p
  (implies (letter-char-p x)
           (characterp x))
  :rule-classes :compound-recognizer)

Subtopics

Letter-charlist-p: (letter-charlist-p x) recognizes lists where every element satisfies letter-char-p.
Letter-chars: A character set for letter-char-p.