Info Catalog eintr: Recursion with list eintr: Recursion eintr: Recursion with cond

eintr: Recursive triangle function

 
 11.3.4 Recursion in Place of a Counter
 --------------------------------------
 
 The ‘triangle’ function described in a previous section can also be
 written recursively.  It looks like this:
 
      (defun triangle-recursively (number)
        "Return the sum of the numbers 1 through NUMBER inclusive.
      Uses recursion."
        (if (= number 1)                    ; do-again-test
            1                               ; then-part
          (+ number                         ; else-part
             (triangle-recursively          ; recursive call
              (1- number)))))               ; next-step-expression
 
      (triangle-recursively 7)
 
 You can install this function by evaluating it and then try it by
 evaluating ‘(triangle-recursively 7)’.  (Remember to put your cursor
 immediately after the last parenthesis of the function definition,
 before the comment.)  The function evaluates to 28.
 
    To understand how this function works, let’s consider what happens in
 the various cases when the function is passed 1, 2, 3, or 4 as the value
 of its argument.
 

Menu

 
· Recursive Example arg of 1 or 2
· Recursive Example arg of 3 or 4
 

Info Catalog eintr: Recursion with list eintr: Recursion eintr: Recursion with cond