Submit first group of exercises

README.md

@@ -1,2 +1,10 @@
 sicp-study-group
 ================
+
+A lay-led study of [SICP](https://mitpress.mit.edu/sicp/) in Berkeley, CA.
+
+* http://www.meetup.com/codeselfstudy/events/187351632/
+* http://www.meetup.com/codeselfstudy/events/187758402/
+* ...
+
+This repo houses my solutions to exercises.

ex1.1.scm

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+;;; Installed Scheme via `brew install mit-scheme` on OS X.
+;;; Running Scheme interpreter in Emacs via `M-x run-scheme`.
+;;; Donny Winston, 2014-06-10
+
+;; MIT/GNU Scheme running under OS X
+;; Type `^C' (control-C) followed by `H' to obtain information about interrupts.
+
+;; Copyright (C) 2014 Massachusetts Institute of Technology
+;; This is free software; see the source for copying conditions. There is NO
+;; warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
+;; PURPOSE.
+
+;; Image saved on Friday May 23, 2014 at 5:50:11 PM
+;;   Release 9.2 || Microcode 15.3 || Runtime 15.7 || SF 4.41 || LIAR/C 4.118
+;;   Edwin 3.116
+
+
+;; Exercise 1.1
+
+1 ]=> 10
+
+;Value: 10
+
+1 ]=> (+ 5 3 4)
+
+;Value: 12
+
+1 ]=> (- 9 1)
+
+;Value: 8
+
+1 ]=> (/ 6 2)
+
+;Value: 3
+
+1 ]=> (+ (* 2 4) (- 4 6))
+
+;Value: 6
+
+1 ]=> (define a 3)
+
+;Value: a
+
+1 ]=> (define b (+ a 1))
+
+;Value: b
+
+1 ]=> (+ a b (* a b))
+
+;Value: 19
+
+1 ]=> (= a b)
+
+;Value: #f
+
+1 ]=> (if (and (> b a) (< b (* a b)))
+          b
+          a)
+
+;Value: 4
+
+1 ]=> (cond ((= a 4) 6)
+            ((= b 4) (+ 6 7 a))
+            (else 25))
+
+;Value: 16
+
+1 ]=> (+ 2 (if (> b a) b a))
+
+;Value: 6
+
+1 ]=> (* (cond ((> a b) a)
+               ((< a b) b)
+               (else -1))
+         (+ a 1))
+
+;Value: 16
+
+1 ]=> 

ex1.2.scm

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+;; Exercise 1.2
+
+(/ (+ 4 5 (- 2 (- 3 (+ 6 (/ 4 5)))))
+   (* 3 (- 6 2) (- 2 7)))
+
+;Value: -37/150

ex1.3.scm

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+;; Exercise 1.3
+
+(define (sum-of-squares x y) (+ (square x) (square y)))
+(define (sum-squares-of-two-largest a b c)
+  (cond ((and (> a c) (> b c)) (sum-of-squares a b))
+        ((and (> a b) (> c b)) (sum-of-squares a c))
+        (else (sum-of-squares b c))))
+
+(= (sum-squares-of-two-largest 3 4 5) (sum-of-squares 4 5))
+(= (sum-squares-of-two-largest 5 4 3) (sum-of-squares 4 5))
+(= (sum-squares-of-two-largest 3 5 4) (sum-of-squares 4 5))

ex1.4.scm

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+;; Exercise 1.4
+
+(define (a-plus-abs-b a b)
+  ((if (> b 0) + -) a b))
+
+;; If b > 0, return `(+ a b)`.
+;; Otherwise, return `(- a b)`.
+;; Thus, return `(+ a (abs b))`,
+;; where `(abs b)` is the absolute value of b.

ex1.5.scm

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+;; Exercise 1.5
+
+;; normal-order evaluation: "fully expand and then reduce"
+;; applicative-order evaluation: "evaluate the arguments and then apply"
+;; Lisp uses applicative-order evaluation, but normal-order can be useful
+;; e.g. for stream processing (to be introduced in Ch 3).
+
+(define (p) (p))
+
+(define (test x y)
+  (if (= x 0)
+      0
+      y))
+
+(test 0 (p))
+
+;; With applicative-order evaluation, the evaluation will never return a value
+;; because `(p)` will never return. With normal-order evaluation, because the
+;; arguments to `test` are not evaluated prior to evaluating the body of `test`,
+;; and because `y` is never evaluated (because `(= x 0)` evaluates to true),
+;; `(test 0 (p))` will return 0.