Merge pull request #8 from jrincayc/example_and_ref_work

Example and ref work

bib.tex

@@ -44,7 +44,7 @@
 \bibitem{SICP}
 Harold Abelson and Gerald Jay Sussman with Julie Sussman.
 {\em Structure and Interpretation of Computer Programs, second edition.}
-MIT Press, Cambridge, 1996.
+MIT Press, Cambridge, \url{https://mitpress.mit.edu/sites/default/files/sicp/index.html}, 1996.
 
 %\bibitem{Bawden88}
 %Alan Bawden and Jonathan Rees.

example.tex

@@ -28,7 +28,7 @@
 (append '(a b) '(c d)) \ev (a b c d)
 \end{scheme}
 
-This procedure returns the first sublist of {\em l} whose car is {\em obj}.
+This procedure returns the first sublist of {\em l} whose car is symbol {\em obj}.
 
 \begin{scheme}
 (define assq (lambda (obj l)
@@ -42,6 +42,23 @@
 (assq 'd e)            \ev \schfalse
 \end{scheme}
 
+This procedure returns the first sublist of {\em l} whose car is symbol or number {\em obj}.
+
+\begin{scheme}
+(define assocns (lambda (obj l)
+  (cond ((null? l) \schfalse)
+        ((and (number? obj) (number? (car (car l)))
+              (= obj (car (car l))))
+         (car l))
+        ((eq? obj (car (car l))) (car l))
+        (else (assocns obj (cdr l)))
+)))
+(define e2 '((a 1) (3 b) (c 4)))
+(assocns 'a e2) \ev (a 1)
+(assocns 3 e2)  \ev (3 b)
+(assocns 1 e2)  \ev \schfalse
+\end{scheme}
+
 This shows using the Y combinator to create a recursive function.
 
 \begin{scheme}