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(librep.info)Accessing List Elements

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Accessing List Elements
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   The most flexible method of accessing an element in a list is via a
combination of the `car' and `cdr' functions. There are other functions
which provide an easier way to get at the elements in a flat list.
These will usually be faster than a string of `car' and `cdr'
operations.

 - Function: nth count list
     This function returns the element COUNT elements down the list,
     therefore to access the first element use a COUNT of zero (or even
     better the `car' function). If there are too few elements in the
     list and no element number COUNT can be found `()' is returned.

          (nth 3 '(0 1 2 3 4 5))
              => 3
          
          (nth 0 '(foo bar)
              => foo

 - Function: nthcdr count list
     This function takes the cdr of the list LIST COUNT times,
     returning the last cdr taken.

          (nthcdr 3 '(0 1 2 3 4 5))
              => (3 4 5)
          
          (nthcdr 0 '(foo bar))
              => (foo bar)

 - Function: last list
     This function returns the last element in the list LIST. If the
     list has zero elements `()' is returned.

          (last '(1 2 3))
              => 3
          
          (last '())
              => ()

 - Function: member object list
     This function scans through the list LIST until it finds an element
     which is `equal' to OBJECT. The tail of the list (the cons cell
     whose car is the matched object) is then returned. If no elements
     match OBJECT then the empty list `()' is returned.

          (member 'c '(a b c d e))
              => (c d e)
          
          (member 20 '(1 2))
              => ()

 - Function: memq object list
     This function is similar to `member' except that comparisons are
     performed by the `eq' function not `equal'.