Lecture 2: Procedures and Recursion
Review:
Self-evaluating expression
#t, 5, “yay”
Name expression
+, foo, bar
N | V
foo | 4
combinations (+ 3 4) to evaluate a combination, sequence of steps:
Evaluate operator
Evaluate arguments
Apply operator value to argument values
Order of evaluation of arguments unspecified, but scheme does it right-to-left
Special forms:
define
(define name value)
(define bar (+ 3 3))
if
(if test consequent alternative)
Make mental pictures for better gasp abstract more difficult to hold
Lambda:
((lambda (x) (* x x)) 5) compound procedure in a combination
↓
(* 5 5) => 25
Lambda procedures are lengthy; in order to reuse over and over again with
simplicity, give name.
(define square
-Æ(lambda (x)
---Æ(* x x)))
Notice indentations
All code now must be tabbed accordingly: newly opened paren is where tab should
begin. In scheme, simply hit the return key and then hit the tab key, and the correct
tab will automatically appear in the code.
Writing Procedures
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