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Defines functors for making modules comparable.
Usage example:
module Foo = struct
module T = struct
type t = ... [@@deriving compare, sexp]
end
include T
include Comparable.Make (T)
end
Then include Comparable.S in the signature
module Foo : sig
type t = ...
include Comparable.S with type t := t
end
To add an Infix submodule:
module C = Comparable.Make (T)
include C
module Infix = (C : Comparable.Infix with type t := t)
A common pattern is to define a module O with a restricted signature. It aims to be (locally) opened to bring useful operators into scope without shadowing unexpected variable names. E.g., in the Date module:
module O = struct
include (C : Comparable.Infix with type t := t)
let to_string t = ..
end
Opening Date would shadow now, but opening Date.O doesn't:
let now = .. in
let someday = .. in
Date.O.(now > someday)
val lexicographic : ('a->'a-> int) list->'a->'a-> int
lexicographic cmps x y compares x and y lexicographically using functions in the list cmps.
val lift : ('a->'a->'result)->f:('b->'a)->'b->'b->'result
lift cmp ~f x y compares x and y by comparing f x and f y via cmp.
val reverse : ('a->'a->'result)->'a->'a->'result
reverse cmp x y = cmp y x
Reverses the direction of asymmetric relations by swapping their arguments. Useful, e.g., for relations implementing "is a subset of" or "is a descendant of".
Where reversed relations are already provided, use them directly. For example, Comparable.S provides ascending and descending, which are more readable as a pair than compare and reverse compare. Similarly, <= is more idiomatic than reverse (>=).
type'a reversed = 'a
reversed is the identity type but its associated compare function is the same as the reverse function above. It allows you to get reversed comparisons with ppx_compare, writing, for example, [%compare: string Comparable.reversed] to have strings ordered in the reverse order.
val compare_reversed : ('a->'a-> int)->'areversed->'areversed-> int
The functions below are analogues of the type-specific functions exported by the Comparable.S interface.
val equal : ('a->'a-> int)->'a->'a-> bool
val max : ('a->'a-> int)->'a->'a->'a
val min : ('a->'a-> int)->'a->'a->'a
Derive Infix or Comparisons functions from just [@@deriving compare], without need for the sexp_of_t required by Make* (see below).