Info Catalog eintr: Loop Example eintr: while eintr: Incrementing Loop

eintr: print-elements-of-list

 
 11.1.2 An Example: ‘print-elements-of-list’
 -------------------------------------------
 
 The ‘print-elements-of-list’ function illustrates a ‘while’ loop with a
 list.
 
    The function requires several lines for its output.  If you are
 reading this in a recent instance of GNU Emacs, you can evaluate the
 following expression inside of Info, as usual.
 
    If you are using an earlier version of Emacs, you need to copy the
 necessary expressions to your ‘*scratch*’ buffer and evaluate them
 there.  This is because the echo area had only one line in the earlier
 versions.
 
    You can copy the expressions by marking the beginning of the region
 with ‘C-<SPC>’ (‘set-mark-command’), moving the cursor to the end of the
 region and then copying the region using ‘M-w’ (‘kill-ring-save’, which
 calls ‘copy-region-as-kill’ and then provides visual feedback).  In the
 ‘*scratch*’ buffer, you can yank the expressions back by typing ‘C-y’
 (‘yank’).
 
    After you have copied the expressions to the ‘*scratch*’ buffer,
 evaluate each expression in turn.  Be sure to evaluate the last
 expression, ‘(print-elements-of-list animals)’, by typing ‘C-u C-x C-e’,
 that is, by giving an argument to ‘eval-last-sexp’.  This will cause the
 result of the evaluation to be printed in the ‘*scratch*’ buffer instead
 of being printed in the echo area.  (Otherwise you will see something
 like this in your echo area:
 ‘^Jgazelle^J^Jgiraffe^J^Jlion^J^Jtiger^Jnil’, in which each ‘^J’ stands
 for a newline.)
 
    In a recent instance of GNU Emacs, you can evaluate these expressions
 directly in the Info buffer, and the echo area will grow to show the
 results.
 
      (setq animals '(gazelle giraffe lion tiger))
 
      (defun print-elements-of-list (list)
        "Print each element of LIST on a line of its own."
        (while list
          (print (car list))
          (setq list (cdr list))))
 
      (print-elements-of-list animals)
 
 When you evaluate the three expressions in sequence, you will see this:
 
      gazelle
 
      giraffe
 
      lion
 
      tiger
      nil
 
    Each element of the list is printed on a line of its own (that is
 what the function ‘print’ does) and then the value returned by the
 function is printed.  Since the last expression in the function is the
 ‘while’ loop, and since ‘while’ loops always return ‘nil’, a ‘nil’ is
 printed after the last element of the list.
 

Info Catalog eintr: Loop Example eintr: while eintr: Incrementing Loop