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Lines

Prefix-lines

Add a prefix to every line in a string.

(prefix-lines x prefix) builds a new string by adding prefix to the start of every line in the string x. The start of x is regarded as the start of a line, and also gets the prefix. For instance,

(prefix-lines "hello world
goodbye world" "  ** ")

Would create the following result:

"  ** hello world
  ** goodbye world"

This is sometimes useful for indenting blobs of text when you are trying to pretty-print things. The operation is fairly efficient: we cons everything into a character list and then coerce it back into a string at the end.

Definitions and Theorems

Function: prefix-lines-aux

(defun prefix-lines-aux (n x xl acc prefix)
  (declare (xargs :guard (and (natp n)
                              (stringp x)
                              (natp xl)
                              (<= n xl)
                              (= xl (length x))
                              (stringp prefix))))
  (let ((n (lnfix n)) (xl (lnfix xl)))
    (if (mbe :logic (zp (- xl n))
             :exec (int= n xl))
        acc
      (let* ((char (char x n))
             (acc (cons char acc))
             (acc (if (eql char #\Newline)
                      (revappend-chars prefix acc)
                    acc)))
        (prefix-lines-aux (+ 1 n)
                          x xl acc prefix)))))

Function: prefix-lines

(defun prefix-lines (x prefix)
  (declare (xargs :guard (and (stringp x) (stringp prefix))))
  (let* ((acc (revappend-chars prefix nil))
         (rchars (prefix-lines-aux 0 x (length x)
                                   acc prefix)))
    (rchars-to-string rchars)))

Theorem: character-listp-of-prefix-lines-aux

(defthm character-listp-of-prefix-lines-aux
  (implies (and (natp n)
                (stringp x)
                (<= n xl)
                (= xl (length x))
                (stringp rprefix)
                (character-listp acc))
           (character-listp (prefix-lines-aux n x xl acc prefix))))

Theorem: stringp-of-prefix-lines

(defthm stringp-of-prefix-lines
  (stringp (prefix-lines x prefix))
  :rule-classes :type-prescription)