Implement 'exact?' and 'inexact?' in Scheme

[Katie Burke]

exact? should return #t if num is exact, #f otherwise.
inexact? should return #t if num is inexact, #f otherwise.
( http://www.scheme.com/tspl4/objects.html#./objects:s86 )

(exact? 1)

Traceback (most recent call last):
File "stdin", line 1, col 2
RunTimeError: unbound variable 'exact?'

(inexact? -123)

Traceback (most recent call last):
File "stdin", line 1, col 2
RunTimeError: unbound variable 'inexact?'