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Pad-trim

Lpadstr

Pad a string with spaces on the left.

(lpadstr x len) extends the string x to length len by adding spaces on the left. For instance,

(lpadstr "foo" 5)
   -->
"  foo"

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: lpadstr

(defun lpadstr (x len)
  (declare (xargs :guard (and (stringp x) (natp len)))
           (type string x)
           (type integer len))
  (mbe :logic
       (implode (lpadchars (explode x) len))
       :exec
       (let* ((x-len (length x))
              (diff (- len x-len)))
         (if (< 0 diff)
             (implode (make-list-ac diff #\Space (explode x)))
           x))))

Theorem: stringp-of-lpadstr

(defthm stringp-of-lpadstr
  (stringp (lpadstr x len))
  :rule-classes :type-prescription)

Theorem: len-of-explode-of-lpadstr

(defthm len-of-explode-of-lpadstr
  (implies (force (stringp x))
           (equal (len (explode (lpadstr x len)))
                  (max (length x) (nfix len)))))

Theorem: streqv-implies-equal-lpadstr-1

(defthm streqv-implies-equal-lpadstr-1
  (implies (streqv x x-equiv)
           (equal (lpadstr x len)
                  (lpadstr x-equiv len)))
  :rule-classes (:congruence))

Theorem: istreqv-implies-istreqv-lpadstr-1

(defthm istreqv-implies-istreqv-lpadstr-1
  (implies (istreqv x x-equiv)
           (istreqv (lpadstr x len)
                    (lpadstr x-equiv len)))
  :rule-classes (:congruence))