Fixnum
An N-bit two's complement integer.
Short-Float
An immediate float format.
Bignum
Bignums are infinite-precision integers, represented somehow.
Floats
Floats are stored as consecutive words of bits.
Ratio
Ratios are stored as two consecutive words of Lisp objects, which should
both be integers.
Complex
Complex numbers are stored as two consecutive words of Lisp objects,
which should both be numbers.