module Incubator:sig..end
val eq_by : ('a -> 'b) -> 'a BatOrd.eq
val comp_by : ('a -> 'b) -> 'a BatOrd.comp
val ord_by : ('a -> 'b) -> 'a BatOrd.ordBuild a eq, cmp or ord function from a projection function.
For example, if you wanted to compare integers based on their
lowest 4 bits, you could write let cmp_bot4 = cmp_by (fun x and use cmp_bot4 as the desired integer
comparator.
-> x land 0xf)