R4RS 6.5.5 (floor number)     ==>  integer
           (ceiling number)   ==>  integer
           (truncate number)  ==>  integer
           (round number)     ==>  integer

These procedures return integers. FLOOR returns the largest integer
not larger than NUMBER. CEILING returns the smallest integer not
smaller than NUMBER. TRUNCATE returns the integer closest to NUMBER
whose absolute value is not larger than the absolute value of NUMBER.
ROUND returns the closest integer to NUMBER, rounding to even when
NUMBER is halfway between two integers.

Rationale: ROUND rounds to even for consistency with the default
rounding mode specified by the IEEE floating point standard.

Note: If the argument to one of these procedures is inexact, then
the result will also be inexact. If an exact value is needed, the
result should be passed to the INEXACT->EXACT procedure.

(floor -4.3)     ==>  -5.0
(ceiling -4.3)   ==>  -4.0
(truncate -4.3)  ==>  -4.0
(round -4.3)     ==>  -4.0

(floor 3.5)      ==>  3.0
(ceiling 3.5)    ==>  4.0
(truncate 3.5)   ==>  3.0
(round 3.5)      ==>  4.0  ; inexact
