Re: [eclipse-clp-users] canonical_path_bug/2 bug on Windows... again

From: Paulo Moura <pmoura_at_...16...>
Date: Tue, 22 May 2012 14:15:33 +0100
Hi Joachim,

Nice to hear from you again.

On 22/05/2012, at 12:16, Joachim Schimpf wrote:

> Paulo Moura wrote:
>> Hi,
>> I'm using ECLiPSe 6.1#112 on Windows 7 64 bits. The built-in predicate canonical_path_bug/2 always seem to return the wrong path when the first argument is an absolute path such as 'C:/Users/' or 'C:\\Users\\'. The returned path always have the current working directory as a prefix. Moreover, if the first argument starts with an environment variable, the variable is not expanded and again the returned path have the current working directory as a prefix. I reported this bug (which was fixed on 5.x) on July 13, 2006.
> 
> Hi Paulo,
> 
> You have overlooked that ECLiPSe internally uses an OS-independent path
> name syntax which employs no separator characters apart from the "/".
> In this syntax, absolute paths always start with a /.
> 
> The ONLY predicate that understands OS-specific path names is
> os_file_name(?EclipseName, ?OSName), which converts between operating
> system syntax and internal Eclipse syntax.  For example, on Windows,
> os_file_name("//C/a/b", "C:\\a\\b") is true.  ALL other built-in
> predicates that accept/return path names, expect/produce the
> simplified internal form.  If you have path names that come in
> OS syntax, you will have to convert them once.
> 
> This is an old (but clean) design decision dating back to the first
> Windows-port of ECLiPSe in the 90s, when there was still much confusion
> about file name syntax in different operating systems.  The kind of "fix"
> you have in mind would break the design.

I find the design sound. In fact, it's a design also adapted by other Prolog compilers. For example, SWI-Prolog provides a similar prolog_to_os_filename/2 built-in predicate (which I use). The only possible issue when using this conversion predicates is when you receive a path, e.g. from a consult/compile/load predicate call, where the user may pass either an operating-system path or a Prolog "internal" path. In my limited test with ECLiPSe 6.1#112, the os_file_name/2 predicate seems behave correctly when the the second argument already uses the internal syntax.

I'm redesigning the Logtalk code that handles operating-system paths to follow more closely this design (the main issue being that only some Prolog compilers provide these conversion predicates).

>  However, I'm open to suggestions
> of how to make things more intuitive and/or nore compatible with other
> systems.


As you know, dealing with file-system is a portability nightmare, specially when considering both POSIX and Windows. The only practical solution will likely be to provide a library that forgoes the native support (from the point-of-view of interface) and provides a portability layer. I have something along these lines in Logtalk:

http://trac.logtalk.org/browser/trunk/examples/cc/osp.lgt
http://trac.logtalk.org/browser/trunk/examples/cc/os.lgt

You may remember contributing to this code in the past. But, currently, the above code is provided as an example of using conditional compilation directives and not as a standard library (this may change on Logtalk 3.x, under development, however). The main reasons are comprehensive testing (specially on Windows), the lack (of up-to-date) binary distributions of the Prolog compilers (e.g. ECLiPSe itself on MacOS X or XSB on Windows), unexpected incompatible changes (e.g. absolute_file_name/2-3 on recent SWI-Prolog and YAP versions), and the commercial nature of some Prolog compilers (I refuse to buy copies given all the work I do for Prolog standardization and to make Logtalk compatible with those compilers). Summarizing what is starting to sound like a rant, such a portable library would need to be actively maintained by the Prolog vendors themselves. I'm skeptical that that will happen any time soon.

Thanks for your support. Cheers,

Paulo


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Paulo Jorge Lopes de Moura, PhD
Assistant Professor
Dep. of Computer Science, University of Beira Interior
6201-001 Covilhã, Portugal

Office 3.18  Ext. 3276
Phone: +351 275 242081 Fax: +351 275 319899
Email: <mailto:pmoura@...16...>

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Research:  <http://logtalk.org/> Blog: <http://blog.logtalk.org/>
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Received on Tue May 22 2012 - 13:15:49 CEST

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