[Caml-list] #use is not textual inclusion

["Richard W.M. Jones" <rich@annexia.org>]

I was trying to break up a large ocaml interpreted script:

  https://github.com/libguestfs/libnbd/blob/master/generator/generator

The script contains sections like:

  module Foo : sig
  (* type signature *)
  end = struct
  (* very long implementation *)
  end

and it would be convenient for me to move the implementations into
separate files.  However this doesn't work:

  module Foo : sig
  (* type signature *)
  end = struct
  #use "implementation.ml"  (* with or without ;; here *)
  end

So I guess #use only works for top level statements, which surprised
me and contradicts the documentation here too:

  https://caml.inria.fr/pub/docs/manual-ocaml/toplevel.html#s%3Atoplevel-directives

I could move the whole module definition to the file, but then I would
lose the advantage of hiding the implementation while keeping the
signature visible in the main file.

Given the constraint that we can't use ocamlc or cppo (because of
minimal build dependencies), are there any alternatives?  My first
thought was C's cpp, but it seems impossible to get that working with
#!/usr/bin/env and preserve the "scriptiness" of being able to just do
./generator/generator to run it.

Rich.