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fib.lisp

 ; Copyright (c) 2008 the authors listed at the following URL, and/or
 ; the authors of referenced articles or incorporated external code:
 ; http://en.literateprograms.org/Fibonacci_numbers_(Lisp)?action=history&offset=20081025104812
 ; 
 ; Permission is hereby granted, free of charge, to any person obtaining
 ; a copy of this software and associated documentation files (the
 ; "Software"), to deal in the Software without restriction, including
 ; without limitation the rights to use, copy, modify, merge, publish,
 ; distribute, sublicense, and/or sell copies of the Software, and to
 ; permit persons to whom the Software is furnished to do so, subject to
 ; the following conditions:
 ; 
 ; The above copyright notice and this permission notice shall be
 ; included in all copies or substantial portions of the Software.
 ; 
 ; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 ; EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 ; MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 ; IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 ; CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 ; TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 ; SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 ; 
 ; Retrieved from: http://en.literateprograms.org/Fibonacci_numbers_(Lisp)?oldid=15288
 
 (defun fib (n)
   "Simple recursive Fibonacci number function"
   (if (< n 2)
     n
     (+ (fib (- n 1)) (fib (- n 2)))))
 
 (defun fib-trec (n)
   "Tail-recursive Fibonacci number function"
   (labels ((calc-fib (n a b)
                      (if (= n 0)
                        a
                        (calc-fib (- n 1) b (+ a b)))))
     (calc-fib n 0 1)))
 
 (defun printfib (start end)
   (format t "(fib-trec ~D)=~D~%" start (fib-trec start))
   (if (< start end)
     (printfib (+ start 1) end)))
 
 (printfib 1 30)