Re: [Chicken-hackers] [PATCH] add pathname-expand

[Mario Domenech Goulart]

Hi Felix and all,

On Mon, 11 Nov 2013 09:36:54 +0100 (CET) Felix Winkelmann <address@hidden> 
wrote:

> From: Mario Domenech Goulart <address@hidden>
> Subject: Re: [Chicken-hackers] [PATCH] add pathname-expand
> Date: Fri, 08 Nov 2013 22:50:47 +0000
>
>> Hi Felix and all,
>> 
>> Sorry for taking so long to handle this issue.  To be honest I'm a bit
>> lost at it (see comments and questions below).
>> 
>> `pathname-expand' looks quite simple at the first sight, but it turns
>> into a can of worms when some corner cases come into play.
>
> Well, if it is such a can of worms, then perhaps it's not such a great
> thing to have, after all. There are so many special cases and platform
> dependencies, that it actually confuses more than it helps.

Getting rid of it is the simplest approach.  There are other ones,
though.  Here are some of them:

* move pathname-expand to an egg.  From users standpoint, I think it
  won't make a big difference between having pathname-expand in the core
  or in an egg.  It's something new anyway.  Having it as an egg can
  actually be a win in the end: it would be available to older chickens
  (although it wouldn't do anything, since pathname expansion is
  implicit).  But at least applications wouldn't break on an "Unbound
  variable: pathname-expand" error.  If pathname-expand is in the core,
  programs that use it will have a hard dependency on CHICKEN 4.9.0.

* make it simpler.  Only expand ~/user.  No ~user and no ~~whatever.

* to work around the issue "what to do when home cannot be determined",
  an additional parameter to determine the default home directory (a
  string) or behavior (a procedure).  Example:

  (define default-user-home-directory
    (make-parameter "/"))

  (define (pathname-expand path)
    (if (home-is-defined?)
        (do-expand path)
        (if (procedure? (default-user-home-directory))
            ((default-user-home-directory) path)
            (do-expand path (default-user-home-directory)))))

  If default-user-home-directory can be a procedure, users may 
  decide what to do when no home is defined.

* combinations of the previous items.

Personally, I'd vote for leaving it out of the core and eventually
implement it as an egg, when we have a consensus on what it should do.

Best wishes.
Mario
-- 
http://parenteses.org/mario