On Sat, 7 Jun 2003, David Brown wrote:

> On Sat, Jun 07, 2003 at 11:08:54AM -0400, Eric C. Cooper wrote:
> 
> > and read_directory path =
> >   let dirh = opendir path in
> >   let rec loop entries =
> >     try match readdir dirh with
> >     | "." | ".." -> loop entries
> >     | filename -> loop (read_filesystem filename :: entries)
> >     with End_of_file -> entries
> >   in
> >   let list = loop [] in
> >   closedir dirh;
> >   list
> 
> But, this isn't tail recursive, so you might as well not pass the
> argument and build up the list upon returning.  Is there a way of making
> it really tail recursive, while using the exception?  It isn't too hard
> with a list ref to accumulate the results.

let read_directory path =
    let dirh = opendir path in
    let rec loop entries =
        let fname, eof = try (readdir dirh), false
                         with End_of_file -> "", true
        in
        if eof then List.rev entries else
        match fname with
            | "." | ".." -> loop entries
            | _ -> loop (fname :: entries)
    in
    loop []

I will also take this opportunity to plug ExtLib.  Using ExtLib you can 
remove the List.rev call, and do something like:

let read_directory path =
    let dirh = opendir path in
    let rec f () = try 
                   match readdir dirh with
                       | "." | ".." -> f()
                       | s -> s
                   with End_of_file -> raise No_more_elements
    in
    ExtList.of_enum (Enum.from f)

Here f is not tail recursive- but it only recurses to get past "." and 
".." files, so it'll never go more than 3 levels deep.  If it bugs you, 
rewrite f in a manner to my first example.

Brian

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