Implement 'integer?', 'rational?', 'real?', and 'complex?' in Scheme

[Katie Burke]

scheme>>> integer? 1901
Traceback (most recent call last):
File "stdin", line 1, col 1
RunTimeError: unbound variable 'integer?'
scheme>>> rational? 1901
Traceback (most recent call last):
File "stdin", line 1, col 1
RunTimeError: unbound variable 'rational?'
scheme>>> real? 1901
Traceback (most recent call last):
File "stdin", line 1, col 1
RunTimeError: unbound variable 'real?'
scheme>>> complex? 1901
Traceback (most recent call last):
File "stdin", line 1, col 1
RunTimeError: unbound variable 'complex?'