[Caml-list] Documentation challenges for the application of comparison functions

[Markus Elfring <Markus.Elfring@web.de>]

Hello,

I have taken another look at a few functions of a software library
where comparison functions should be passed.

…
let rec find ~cmp x = function
    Empty -> raise Not_found
  | …

let not_found_default_action ~value ?compare:(cmp=Stdlib.compare) =
    raise Not_found
…


Interface descriptions can be generated then in a known format for OCaml 4.11.1.

…
val find : cmp:('a -> 'b -> int) -> 'a -> ('b, 'c) t -> 'c
val not_found_default_action : value:'a -> ?compare:('b -> 'b -> int) -> 'c
…


Now I find two details interesting for further clarification.

1. The first reference for a comparison function seems to express a need for
   different data types “'a” and “'b” while a single type might be sufficient
   for the comparison function according to the second function.

2. The specification of “Stdlib.compare” looks clear according to the semantics
   for a default parameter in a ML source file while the OCaml arrow representation
   can look more challenging.
   How would you recognise that such a function parameter should be applied
   for comparison calls?

Regards,
Markus