lucy:~/451> scheme-elk
> (+ 2 3)
5
> (+ 6 (* 3 5))
21
> (if (> 1 2) 100 10)
10
> (if (> 1 2) 100)
()
> (car (1 2 3 4 5))
car: application of non-procedure: 1
1> (car '(1 2 3 4 5))
1
1> (cdr '(1 2 3 4 5))
(2 3 4 5)
1> (load "functions.scm")

1> (square 20)
400
1> (sum '(1 2 3 4 5))
15
1> (sum '())
0
1> (mymap square '(1 2 3))
(1 4 9)
1> (load "primes.scm")

1> (map isprime '(1 2 3 4 5 6 7 8 9 10))
(#f #t #t #f #t #f #t #f #f #f)
1> (quit)
lucy:~/451>

functions.scm

; squares its argument
(define square
  (lambda (x)
    (* x x)
  )
)

; sums all integers in a list
(define sum
  (lambda (l)
    (if (null? l)
	0
	(+ (car l) (sum (cdr l)))
    )
  )
)

; applies a 1-place function to a list of arguments (like built-in map)
(define
  (mymap f l)
  (if (null? l)
      l
      (cons (f (car l)) (mymap f (cdr l)))))

primes.scm

; determines if a divides b (if there is an integer k s.t. b = a*k)
(define divides
  (lambda (a b)
    (if (= a 0) (= b 0) (if (= (modulo b a) 0) #t #f))
  )
) 

; given odd f & x, determines if there's a factor y of x s.t. f <= y <= sqrt(x)
(define findfactor
  (lambda (x f)
    (cond 
     ((> (* f f) x) #f) 
     ((divides f x) #t)
     (else (findfactor x (+ f 2)))
    )
  )
)

; given an integer x, determines if x is prime
(define isprime
  (lambda (x)
    (cond
     ((< x 2) #f)
     ((= x 2) #t)
     ((and (> x 2) (divides 2 x)) #f)
     (else (not (findfactor x 3)))
    )
  )
)