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Compare

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`Compare`

Monomorphic comparison for common ground types and common type constructors.

Compare provides a module signature for the standard comparison functions and operators as well as modules of that signature for the common OCaml ground types (int, bool, etc.) and type constructors (list, option, etc.).

Compare also provides some additional helpers for comparison-related tasks.

Signatures and a functor

module type COMPARABLE = sig ... end

COMPARABLE is a signature for basic comparison. It is used only for instantiating full comparison modules of signature S via the functor Make.

module type S = sig ... end

S is a signature for a fully-fledge comparison module. It includes all the functions and operators derived from a compare function.

module Make (P : COMPARABLE) : S with type t := P.t

Base types

The specialised comparison and all the specialised functions and operators on the base types are compatible with the polymorphic comparison and all the polymorphic functions and operators from the Stdlib.

module Char : S with type t = char

module Bool : S with type t = bool

module Int : sig ... end

Int is a comparison module. Out of performance concerns, the signature actually contains compiler builtins (external) rather than val.

module Int32 : S with type t = int32

module Uint32 : S with type t = int32

module Int64 : S with type t = int64

module Uint64 : S with type t = int64

module String : S with type t = string

module Bytes : S with type t = bytes

module Z : S with type t = Z.t

Z is a comparison module for Zarith numbers.

module Q : S with type t = Q.t

Q is a comparison module for Zarith rationals.

Type constructors

Provided the functor argument(s) are compatible with the polymorphic comparison of the Stdlib, then the specialised comparison and all the specialised functions and operators on the derived types are compatible with the polymorphic comparison and all the polymorphic functions and operators from the Stdlib.

module List (P : COMPARABLE) : S with type t = P.t list

module Option (P : COMPARABLE) : S with type t = P.t option

module Result
  (Ok : COMPARABLE)
  (Error : COMPARABLE) : 
  S with type t = (Ok.t, Error.t) Pervasives.result

List lengths

Helpers for more readable Stdlib.List.compare_lengths and Stdlib.List.compare_length_with.

These modules are intended to be used as Module.(expression), most often within an if condition. E.g.,

if Compare.List_length_with.(chunks > max_number_of_chunks) then
   raise Maximum_size_exceeded
else
   ..

module List_length_with : sig ... end

module List_lengths : sig ... end

Building blocks

val or_else : int -> (unit -> int) -> int

or_else c f is c if c <> 0 or f () otherwise.

The intended use is

let compare (foo_a, bar_a) (foo_b, bar_b) =
  or_else (Foo.compare foo_a foo_b) (fun () -> Bar.compare bar_a bar_b)