Scheme Programming Idioms

Life is hard. Can't get to heaven on roller skates.
-Timbuk Three

• Remember, every Scheme expression returns a value!

• This means almost always when you want to ``leave off'' the else clause of an if, what you really want to do is return 0 or return the empty sentence or such.

• Test your code! There is no excuse for not testing.

• If you can't think of how to write a function, type in some test cases. Might give you ideas.

• Remember to test the boundary cases. This is the best way to find bugs, and also a good way to uncover the right base case for a recursive definition.

This code	Can be replaced by this
(if test #t #f)	test
(if test #f #t)	(not test)
(if foo bar #f)	(and foo bar)
(if foo #t bar)	(or foo bar)
(if test x (+ x y))	(+ x (if test y 0))
(if test (word w '-suffix) w)	(word w (if test '-suffix ""))
(every (lambda (x)           (if (test? x) x '()))        sen)	(keep test? sen)
(if test (begin foo bar))	(cond (test foo bar))
(lambda (x) (proc x))	proc
(cond ((equal? letter 'a) #t) ((equal? letter 'e) #t) ((equal? letter 'i) #t) ((equal? letter 'o) #t) ((equal? letter 'u) #t) (else #f)))	(or (equal? letter 'a) (equal? letter 'e) (equal? letter 'i) (equal? letter 'o) (equal? letter 'u))
(or (equal? letter 'a) (equal? letter 'e) (equal? letter 'i) (equal? letter 'o) (equal? letter 'u))	(member? letter '(a e i o u))
(= (count foo) 0)	(empty? foo)
(= (count foo) 1)	(empty? (butfirst foo))

Send me more and I'll put them in.