Re: [Caml-list] Some/None

[Oliver Bandel <oliver@first.in-berlin.de>]

On Thu, 25 Apr 2002, John Max Skaller wrote:

> Oliver Bandel wrote:
> 
> >Does it make sense to give back None/Some
> >out of a function 
> >
> Oh yes! I do this all the time, lots and lots.
> 
> Consider
> 
[...]
> which searches a list for a number x,
> and returns its position n as 
> 
>   Some n 
> 
> if it is found in the list, or
> 
>   None
> 
> if it isn't: its position in the list is None,
> it doesn'tr have a position, or Some position
> if it does.

OK, that makes sense to me. :)

> 
> >(e.g. is_regularfile/is_directory/...)
> >
> 
> What you want here is:
> 
>     type file_type_t = Regular | Directory | Special | Root | NonExistant

Wow!

Good idea. So I don't rely on the predefined type and use my own :)
That's fine.


> 
>    let file_type (s:string): file_type_t =
> 
>     (code to find the file type here) ...

OK :)

let type_of_file (name:string) =
     try (
           match (Unix.stat name).Unix.st_kind
           with
           | Unix.S_REG   -> Regular
           | Unix.S_DIR   -> Directory
           | Unix.S_CHR   -> Special
           | Unix.S_BLK   -> Special
           | Unix.S_LNK   -> Special (* ok, on ENOENT Unix.lstat *)
           | Unix.S_FIFO  -> Special
           | Unix.S_SOCK  -> Special
         )
      with 
      | Unix.Unix_error (Unix.ENOENT,_,_) -> NonExistant (* maybe link-problem => Unix.lstat *)


So this makes completely sense.


[...]
>     type file_data =
>       | Regular of int (* file size in megs *)
>       | Directory of int (* number of entries *)
>       | Special
>     ....

nice idea. :)


Thanks,
   Oliver

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