Ordering is intended to make code that matches on the result of a comparison
more concise and easier to read. For example, one would write:
match Ordering.of_int (compare x y) with | Less -> ... | Equal -> ... | Greater -> ...
let r = compare x y in if r < 0 then ... else if r = 0 then ... else ...
of_int n is:
Less if n < 0 Equal if n = 0 Greater if n > 0
to_int t is:
Less -> -1 Equal -> 0 Greater -> 1
It can be useful when writing a comparison function to allow one to return
Ordering.t values and transform them to