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(cl)Searching Sequences

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Searching Sequences
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These functions search for elements or subsequences in a sequence.
(See also `member*' and `assoc*'; Note: Lists.)

 - Function: find item seq &key :test :test-not :key :start :end
          :from-end
     This function searches SEQ for an element matching ITEM.  If it
     finds a match, it returns the matching element.  Otherwise, it
     returns `nil'.  It returns the leftmost match, unless `:from-end'
     is true, in which case it returns the rightmost match.  The
     `:start' and `:end' arguments may be used to limit the range of
     elements that are searched.

 - Function: position item seq &key :test :test-not :key :start :end
          :from-end
     This function is like `find', except that it returns the integer
     position in the sequence of the matching item rather than the item
     itself.  The position is relative to the start of the sequence as
     a whole, even if `:start' is non-zero.  The function returns `nil'
     if no matching element was found.

 - Function: count item seq &key :test :test-not :key :start :end
     This function returns the number of elements of SEQ which match
     ITEM.  The result is always a nonnegative integer.

   The `find-if', `find-if-not', `position-if', `position-if-not',
`count-if', and `count-if-not' functions are defined similarly.

 - Function: mismatch seq1 seq2 &key :test :test-not :key :start1 :end1
          :start2 :end2 :from-end
     This function compares the specified parts of SEQ1 and SEQ2.  If
     they are the same length and the corresponding elements match
     (according to `:test', `:test-not', and `:key'), the function
     returns `nil'.  If there is a mismatch, the function returns the
     index (relative to SEQ1) of the first mismatching element.  This
     will be the leftmost pair of elements which do not match, or the
     position at which the shorter of the two otherwise-matching
     sequences runs out.

     If `:from-end' is true, then the elements are compared from right
     to left starting at `(1- END1)' and `(1- END2)'.  If the sequences
     differ, then one plus the index of the rightmost difference
     (relative to SEQ1) is returned.

     An interesting example is `(mismatch str1 str2 :key 'upcase)',
     which compares two strings case-insensitively.

 - Function: search seq1 seq2 &key :test :test-not :key :from-end
          :start1 :end1 :start2 :end2
     This function searches SEQ2 for a subsequence that matches SEQ1
     (or part of it specified by `:start1' and `:end1'.)  Only matches
     which fall entirely within the region defined by `:start2' and
     `:end2' will be considered.  The return value is the index of the
     leftmost element of the leftmost match, relative to the start of
     SEQ2, or `nil' if no matches were found.  If `:from-end' is true,
     the function finds the _rightmost_ matching subsequence.