#|

Simple program to illustrate recursive processing.

Look to see if some symbol is in a list. |#


(setf our-list
      '(The other two slight air and purging fire
	Are both with thee wherever I abide The first
	my thought the other my desire
	These present-absent with swift motion slide
	For when these quicker elements are gone))


(defun word-present (word l) ; <-- Note: "l" as in list, not 1 as in 1,2,3
  (cond
    ((null l) 'not-present)                ; On the condition that the list is empty BASE CASE
    ((equal word (first l)) 'yes-present)  ; If the first word is what we are looking for, PRESENT, BASE CASE
    (t (word-present word (rest l)))))     ; Otherwise look in the remainder of the list. RECURSIVE CASE

(format t "~%To run: (word-present 'desire our-list) and (word-present 'elephant our-list)~%")

#| Output:

CL-USER(41): (word-present 'desire our-list)
YES-PRESENT

CL-USER(42): (word-present 'elephant our-list)
NOT-PRESENT

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