Re: [PATCH] gnu: graphviz: Enable Guile library.

[Roel Janssen <roel@gnu.org>]

Hello Danny,

Thank you for your elaborate response.  This makes it quite easy for me
to write the module file.  I added "write" and "rm" to the module, which
should make it complete.

What is the preferred way to include the module file to the package?
Should I create another package with this file alone, and use it as a
propagated input for graphviz?

Kind regards,
Roel Janssen


Danny Milosavljevic writes:

> Hi,
>
> On Mon, 09 May 2016 22:54:00 +0200
> Roel Janssen <roel@gnu.org> wrote:
>
>> it is automatically generated using SWIG.  I had to experiment a bit to
>> find out that the functions exposed in Guile did not have a namespace (gv.).
>
> You can add a prefix when importing, so the symbols of the module shouldn't have a prefix - the user would end up with two prefixes (or would have to cut the other prefix out and replace it or something).
>
>      (use-modules ((gdb) #:renamer (symbol-prefix-proc 'gdb:)))
>
> See also <http://www.swig.org/Doc2.0/Guile.html>.
>
>> There are functions called "rm" and "write" which are obviously already
>> used for other purposes in Scheme.  These functions will have to be
>> renamed or just left out of the Scheme module.  
>
> The user can specify which symbols to import (and also rename stuff there if needed) so I'd do nothing of the sort.
>
>      (use-modules ((ice-9 popen)
>                    #:select ((open-pipe . pipe-open) close-pipe)
>                    #:renamer (symbol-prefix-proc 'unixy:)))
>
> It's true that people still use the form
>
>    (use-modules (xxx))
>
> without specifying what the final imported symbols are, but that's something I consider bad practise in most cases (in any language - hey let's import random stuff into my namespace and have which module it gets each function from change on each package update. How about no?).
>
> For example, let's say you have two modules "a" and "b".
> Let module "a" contain "select".
> Let module "b" contain "write".
>
> Let's say you use it as
>
> (use-modules (a) (b))
>
> ; main program
> (write ...)
> (select ...)
>
> Then it will use b's write, a's select in your program, repectively. Say you release it and people use it. 
>
> Now let's say someone devious (not really, it can make sense to him) adds "select" to module "b". Suddenly your program will use b's select *even though you didn't change anything in it*. 
>
> Bad.
>
> A complete set to try this:
>
> $ export GUILE_LOAD_PATH=.
>
> ;;; a.scm
> (define-module (a) #:export (select))
> (define (select) (display "a.select") (newline))
>
> ;;; b.scm
> (define-module (b) #:export (write select))
> (define (write) (display "b.write") (newline))
> (define (select) (display "b.select") (newline))
>
> ;;; main.scm
> (use-modules (a) (b))
> (write)
> (select)
>
> Note that you do get warnings by guile
>
> WARNING: (guile-user): imported module (a) overrides core binding `select'
> WARNING: (guile-user): `select' imported from both (a) and (b)
> b.select
> WARNING: (guile-user): imported module (b) overrides core binding `write'
> b.write
>
> ... which is nice.