Info Catalog eintr: Incrementing Loop Details eintr: while

eintr: Decrementing Loop

 
 11.1.4 Loop with a Decrementing Counter
 ---------------------------------------
 
 Another common way to write a ‘while’ loop is to write the test so that
 it determines whether a counter is greater than zero.  So long as the
 counter is greater than zero, the loop is repeated.  But when the
 counter is equal to or less than zero, the loop is stopped.  For this to
 work, the counter has to start out greater than zero and then be made
 smaller and smaller by a form that is evaluated repeatedly.
 
    The test will be an expression such as ‘(> counter 0)’ which returns
 ‘t’ for true if the value of ‘counter’ is greater than zero, and ‘nil’
 for false if the value of ‘counter’ is equal to or less than zero.  The
 expression that makes the number smaller and smaller can be a simple
 ‘setq’ such as ‘(setq counter (1- counter))’, where ‘1-’ is a built-in
 function in Emacs Lisp that subtracts 1 from its argument.
 
    The template for a decrementing ‘while’ loop looks like this:
 
      (while (> counter 0)                    ; true-or-false-test
        BODY...
        (setq counter (1- counter)))          ; decrementer
 

Menu

 
· Decrementing Example        More pebbles on the beach.
· Dec Example parts           The parts of the function definition.
· Dec Example altogether      Putting the function definition together.
 

Info Catalog eintr: Incrementing Loop Details eintr: while