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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)