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• Pad-trim

Lpadchars

Pad a character-list with spaces on the left.

(lpadchars x len) extends the character list x to length len by adding spaces on the left. For instance,

(lpadchars '(#\f #\o #\o) 5)
   -->
'(#\Space #\Space #\f #\o #\o)

This is completely dumb: we don't try to account for newlines, tabs, or anything like that, and just add #\Space characters until reaching the desired width.

If no new spaces are needed, x is returned unchanged and no consing is performed.

Definitions and Theorems

Function: lpadchars

(defun lpadchars (x len)
  (declare (xargs :guard (and (character-listp x) (natp len)))
           (type integer len))
  (mbe :logic
       (append (repeat (nfix (- (nfix len) (len x)))
                       #\Space)
               (make-character-list x))
       :exec
       (let* ((x-len (length x))
              (diff (- len x-len)))
         (if (< 0 diff)
             (make-list-ac diff #\Space x)
           x))))

Theorem: character-listp-of-lpadchars

(defthm character-listp-of-lpadchars
  (character-listp (lpadchars x len)))

Theorem: len-of-lpadchars

(defthm len-of-lpadchars
  (equal (len (lpadchars x len))
         (max (len x) (nfix len))))

Theorem: charlisteqv-implies-equal-lpadchars-1

(defthm charlisteqv-implies-equal-lpadchars-1
  (implies (charlisteqv x x-equiv)
           (equal (lpadchars x len)
                  (lpadchars x-equiv len)))
  :rule-classes (:congruence))

Theorem: icharlisteqv-implies-icharlisteqv-lpadchars-1

(defthm icharlisteqv-implies-icharlisteqv-lpadchars-1
  (implies (icharlisteqv x x-equiv)
           (icharlisteqv (lpadchars x len)
                         (lpadchars x-equiv len)))
  :rule-classes (:congruence))