exercises and notes from "Gentle introduction"

vars-and-effects.lisp

@@ -0,0 +1,94 @@
+;; setq defvar defun - examples of sideffectful things
+
+(random 100)
+
+;; setq could even change local variables (defined by function arguments)
+(defun bad-style (p)
+  "This function will overdefine it's input P."
+  (setf p (+ p 2))                      ; changes local variable
+  (setf r (* p 2))
+  `(result is ,p))
+
+p                                       ; this is not set by the setf
+r                                       ; this global value is changed
+
+(bad-style 15)
+
+;; wait, there's setf, what's different in setq?
+;; setf has "place" as first item, so setter forms
+
+(documentation `setf `function)
+(documentation `setq `function)
+
+(apropos "random")
+
+;;; exercises
+
+(defun throw-die ()
+  (+ 1 (random 6)))
+(throw-die)
+
+(defun throw-dice ()
+  (list (throw-die) (throw-die)))
+(throw-dice)
+
+(defun snake-eyes-p (thro)
+  (equal thro `(1 1)))
+(snake-eyes-p `(1 1))
+(snake-eyes-p `(1 2))
+
+(defun boxcars-p (thro)
+  (equal thro `(6 6)))
+(boxcars-p `(6 6))
+(boxcars-p `(1 2))
+
+(funcall `+ `(1 2))                       ; 149
+(apply `+ `(1 2 5))
+
+(defun instant-win-p (the-throw)
+  (let ((win-hands `(7 11))
+        (sum (apply #'+ the-throw)))
+    (member sum win-hands)))
+
+(defun instant-loss-p (the-throw)
+  (let ((loose-hands `(2 3 12))
+        (sum (apply #'+ the-throw)))
+    (member sum loose-hands)))
+;;; breaking my head, looking for #'contains function for list
+;;; apropos doesn't quite help
+(member 7 (list 1 4 7 11))              ; well, member returns "rest"
+
+(instant-win-p `(6 5))                  ; so, this is correct. cool
+(or `t nil)
+
+(instant-loss-p `(6 5))
+
+(defun say-throw (the-throw)
+  (cond ((equal the-throw `(1 1)) `snake-eyes)
+        ((equal the-throw `(6 6)) `boxcars)
+        (t (apply #'+ the-throw))))
+(say-throw '(1 1))
+(say-throw '(6 6))
+(say-throw '(2 5))
+
+;; firsth throw either insta-win, insta-loose, or set point
+(defun craps ()
+  (let* ((the-throw (throw-dice ))
+         (result (cond ((instant-loss-p the-throw) `(,(say-throw the-throw) -- you loose))
+                       ((instant-win-p the-throw) `(,(say-throw the-throw) -- you win))
+                       (t `(your point is ,(say-throw the-throw))))))
+    (append `(throw ,(first the-throw) and ,(second the-throw) -- ) result)))
+
+(craps)
+
+(defun try-for-point (point)
+  (let* ((the-throw (throw-dice))
+         (value (apply #'+ the-throw))
+         (result (cond ((equal value point) `(you win))
+                       ((equal value 7) `(you loose))
+                       (t `(throw again)))))
+    (append `(throw ,(first the-throw) and ,(second the-throw) -- ,value --) result)))
+
+(try-for-point 8)
+
+;; next onto the 6, list data structures