Christophe Rhodes  <csr21@cam.ac.uk> wrote:
+---------------
| rpw3@rpw3.org (Rob Warnock) writes:
| > (defun prefix-match-p (prefix line)
| >   (not (mismatch prefix line :end2 (length prefix) :test #'char-equal)))
| 
| I think you need
| (defun prefix-match-p (prefix line)
|   (and (>= (length line) (length prefix))
|        (not (mismatch prefix line :end2 (length prefix) :test #'char-equal))))
| otherwise you run the risk of signalling an error, which isn't what
| you want, when the argument to END2 is larger than the length of the line.
+---------------

Oops! Correct, good point.

+---------------
| That can also be written
|   (defun prefix-match-p (prefix line)
|     (let ((mismatch (mismatch prefix line :test #'char-equal)))
|       (or (null mismatch) (= mismatch (length prefix)))))
+---------------

O.k., but to my taste this is slightly simpler:

    (defun prefix-match-p (prefix line)
      (not (mismatch prefix line :end2 (min (length prefix) (length line))
				 :test #'char-equal)))


-Rob

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