regexps that match and don't match

[Emanuel Berg]

Did anyone think of doing something like this?

    (defun re-match-white-black (string re-white re-black)
      (let ((white (string-match re-white string))
            (black (string-match re-black string)) )
        (and white (not black)) ))
    ;; (re-match-white-black "aaab" ".*b" "z.*") ; t
    ;; (re-match-white-black "baab" ".*b" "z.*") ; t
    ;; (re-match-white-black "aaac" ".*b" "z.*") ; nil
    ;; (re-match-white-black "zaab" ".*b" "z.*") ; nil
    ;; (re-match-white-black "zaac" ".*b" "z.*") ; nil

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