COM 1358 Assignment #2.
Due: Tuesday, 18 April 2000

For these programming exercises, just turn in the code for your
solution.  Your code should be written in the functional subset
of R5RS Scheme, augmented by DEFINE-DATATYPE and CASES.  Your
code should contain no exclamation points or i/o, and must define
all procedures that are not standard in R5RS Scheme.

Programming exercises:

1.  Implement a procedure SELECT that takes a predicate and a list,
    and returns the first element of the list that satisfies the
    predicate, or #F if none of the elements satisfy the predicate.
    Examples:

        > (select negative? '(1 3 5))
        #f
        > (select symbol? (list + (exp 1) 'pie 'r "round"))
        pie

2.  Implement a procedure REDUCE-LEFT that takes a binary procedure f,
    an initial value x0, and a possibly empty list (x1 ... xn), and
    returns x0 if the list is empty, or the value obtained by calling
    REDUCE-LEFT on f, (f x0 x1), and the list (x2 ... xn) if the list
    is nonempty.  Examples:

        > (reduce-left * 1 '(1 2 3 4 5 6 7 8 9 10))
        3628800
        > (reduce-left (lambda (x y) (cons y x)) '() '(a b c d e))
        (e d c b a)

Exercise 2.2.1 (without using VECTOR->LIST)
Exercise 2.2.2
Exercise 2.3.3 (without using REVERSE or LIST->VECTOR)