Module Tablecloth.Comparator

Comparator provide a way for custom data structures to be used with Maps and Sets

Say we have a module Book which we want to be able to create a Set of

  module Book = struct
    type t = {
      isbn: string;
      title: string;
    }

    let compare bookA bookB =
      String.compare bookA.isbn bookb.isbn
  end

First we need to make our module conform to the S signature.

This can be done by using the Make functor.

  module Book = struct
    type t = {
      isbn: string;
      title: string;
    }

    let compare bookA bookB =
      String.compare bookA.isbn bookb.isbn
    
    include Comparator.Make(struct 
      type nonrec t = t

      let compare = compare
    end)
  end

Now we can create a Set of books

  Set.fromList (module Book) [
    { isbn="9788460767923"; title="Moby Dick or The Whale" }
  ]