RE: [Caml-list] Type Encoding Format Control

[David Allsopp <dra-news@metastack.com>]

Kenneth Adam Miller wrote:
> In the case of 2), that's interesting because such a type of
> Some None is sort of antithetical to describing anything 
> sensical. Not that it's not pragmatic or doesn't occur-I'm sure
> some functions get combined in ways that stuff like this crops 
> up. But I think of the typing system as being badly exercised 
> if something like this arises-

One example that springs immediately to mind: NULLable field in a database, so 'a option is a sensible type to represent it. Now consider a function intended to generate SQL UPDATE statements for that field:

val update_record : ?foo:int option -> ?bar:int option -> id:int -> baz:string -> bool

where omitting ~foo or ~bar means "don't change foo/bar in the UPDATE statement". Within the code for update_record:

foo = None => don't update that field
foo = Some None => set that field to NULL
foo = Some (Some i) => set that field's value to i

and all three cases will need different code.

See also https://github.com/ocaml/ocaml/blob/trunk/typing/env.ml#L391

What's (to you) badly exercised or nonsensical in either of those representations?


David