In OCaml, you can nest signatures:
module type FOO =
sig
module type BAR
(* … *)
end
I was just wondering if anyone had any examples of this in use, since I can’t think of any places where it would be needed. I imagine it’s probably useful in the return signatures of functors, but I can’t think of any specific things.
First example which came to my mind : http://caml.inria.fr/pub/docs/manual-ocaml/libref/type_Map.html
(it's indeed a functor signature)
I recall seeing a few modules (maybe in batteries), that included an Infix module inside that could be opened separately and only when truly wanted. For example,
module Rational =
struct
let add a b = ...
let sub a b = ...
module Infix =
struct
let (<+>) = add
let (<->) = sub
end
end
In this way if you were to open the Rational.Infix module, you wouldn't de-scope(?) any functions with the same names as anything in Rational.
I am working on a project where we use modules to demarcate types. Having a module define only one type and manipulate that type helps in organization; especially when the modules are small and having a separate file wouldn't be advantageous, and variant types don't make sense.
module Node =
struct
end
module Edge =
struct
end
type 'a tree = { nodes : 'a Node.t; edges : 'a Edge.t; }
We also use them, although as separate files (combined with -mlpack), for all the parsers we need for biological data --Nexus, Fasta, Phylip, et cetera.
Lastly, often when prototying a new algorithm we will write it in ocaml first, then work on a C version. We usually keep the ocaml version in a inner module with the same function names.
module Align =
struct
module OCaml =
struct
end
end
