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Char-fix

Coerce to a character.

(char-fix x) is the identity on characters, and returns the NUL character (i.e., the character whose code is 0) for any non-character.

This is similar to other fixing functions like fix and nfix. See also chareqv.

Function: char-fix$inline

(defun char-fix$inline (x)
  (declare (xargs :guard t))
  (if (characterp x) x (code-char 0)))

Theorem: characterp-of-char-fix

(defthm characterp-of-char-fix
  (characterp (char-fix x))
  :rule-classes :type-prescription)

Theorem: char-fix-default

(defthm char-fix-default
  (implies (not (characterp x))
           (equal (char-fix x) (code-char 0))))

Theorem: char-fix-when-characterp

(defthm char-fix-when-characterp
  (implies (characterp x)
           (equal (char-fix x) x)))