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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))