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; HW03.lisp - Homework Assignment #3 for CS408, Fall Quarter, 2006

; Copyright (c) 2006 Ira W. Snyder (devel@irasnyder.com)

;

; 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.

;;; Problem 1

(defun PALINDROME (LI)

  (append LI (reverse LI))

)

;;; Problem 2

(defun PALINDROMEP (LI)

  ; define a local function so we can do this tail-recursively

  (labels ((PAL-HELP (L1 L2)

              (cond

                ((null L1) t)

                ((equal (car L1) (car L2)) (PAL-HELP (cdr L1) (cdr L2)))

                (t                        nil)

              )

            ))

    ; call the tail-recursive local function

    (PAL-HELP LI (reverse LI))

  )

)

;;; Problem 3

(defun DIVISIBLE-BY-N (DIVIDEND DIVISOR)

  (cond

    ((= (mod DIVIDEND DIVISOR) 0) t)

    (t                            nil)

  )

)

;;; Problem 4

(defun SQUASH (LI)

  (cond

    ((null LI) nil)

    ((atom LI) (list LI))

    (t         (append (SQUASH (car LI)) (SQUASH (cdr LI))))

  )

)

;;; Problem 5

(defun COUNT-ATOMS (LI)

  (cond

    ((null LI) 0)

    ((atom LI) 1)

    (t         (+ (COUNT-ATOMS (car LI)) (COUNT-ATOMS (cdr LI))))

  )

)

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