CL-Pattern-Matching

let-match

CL-USER> (let-match ((1 2 ?three) '(1 2 3))
           (* ?three ?three))
9
T
CL-USER> (let-match ((1 2 ?three) '(3 2 1))
           (* ?three ?three))
NIL
NIL
CL-USER> (let-match ((1 2 ?three) '(1 2 3))
           nil)
NIL
T

cond-match

CL-USER> (defvar form nil)
FORM
CL-USER> (cond-match form
           (nil "Nil!")
           (1 "One!")
           (?x ?x))
"Nil!"
CL-USER> (setf form 1)
1
CL-USER> (cond-match form
           (nil "Nil!")
           (1 "One!")
           (?x ?x))
"One!"
CL-USER> (setf form "Yo mama!")
"Yo mama!"
CL-USER> (cond-match form
           (nil "Nil!")
           (1 "One!")
           (?x ?x))
"Yo mama!"

defun-match

CL-USER> (defun-match desc-args
           (nil "No args!")
           ((?x) "One argument!")
           ((?x ?y) "Two arguments!")
           ((?x ?y . ?z) "More than two arguments!"))
DESC-ARGS
CL-USER> (desc-args)
"No args!"
CL-USER> (desc-args 1)
"One argument!"
CL-USER> (desc-args 1 2)
"Two arguments!"
CL-USER> (desc-args 1 2 3)
"More than two arguments!"
CL-USER> (defun-match my-map
           ((?fn nil) nil)
           ((?fn (?car . ?cdr)) (cons (funcall ?fn ?car)
                                      (my-map ?fn ?cdr))))
MY-MAP
CL-USER> (my-map #'(lambda (x) (* x x))
                 '(1 2 3 4 5 6))
(1 4 9 16 25 36)
CL-USER> (defun-match factorial
           ((0) 1)
           ((?x) (* ?x (factorial (- ?x 1)))))
FACTORIAL
CL-USER> (factorial 1)
1
CL-USER> (factorial 3)
6
CL-USER> (factorial 5)
120
CL-USER> (factorial 7)
5040