Re: hobbit problems

[Bernard URBAN <Bernard.Urban@meteo.fr>]

>>>>> "thi" == thi  <ttn@mingle.glug.org> writes:

    thi> Bernard URBAN writes:
    >> The way intern and friends work is also largely mysterious to
    >> me.  Added to module, it is a real nightmare. For the sake of
    >> hobbit, having intern well explained and a C interface to
    >> modules would help a lot. If anyone is listening to that...

    thi> From ghobbit.h, we have

    thi> #define intern(x,y) scm_permanent_object(scm_intern((x),(y)))

This is actually in guile-hobbit-1.3 and above:
#define intern(x,y) scm_permanent_object(scm_sysintern0((x)))
and something more complex in the case of modules (see below why).
In the file libguile/symbols.c, there are also a lot of other "intern"
variants, which usefulness is unclear to me. 

There is also 
#define intern_symb(x,y) scm_permanent_object(scm_intern((x),(y)))
in guilehob.h, and the distinction was necessary until now, but I
don't know why. This is a SCM legacy,
present since the original hobbit.

    thi> The function scm_intern() is defined in libguile/symbols.c,
    thi> and takes symbol name (as char *) and length.  The symbol is
    thi> hashed into obarray `scm_symhash', then bound to a newly
    thi> created variable.  Finaly, the pair

    thi> 	(NAME . VALUE)

    thi> is returned.  If the symbol was already in the obarray, its
    thi> name and value are used immediately (w/o creating a new
    thi> variable).  This is why the alias `my_car' looks at the `cdr'
    thi> of the call to `intern'.

    thi> Because the C macro `intern' uses `scm_intern', there is no
    thi> module interaction; whoever has access to `scm_symhash' can
    thi> see the symbol/variable.  Whether or not this means that
    thi> hobbit runtime needs to be in the module that sees
    thi> `scm_symhash' is not known to me.

If scm_symhash is only accessed through an intern-like function, it is
irrelevant.

The basic problem is that in most cases (at least in guile-1.3), you
have some useful symbols in some module. You cannot only rely on
"intern" to see if a symbol is still defined. Hence the compilation with -m
and the macro #ifdef HOBBIT_MODULE, which is a kludge. So the need of
a C interface to the module system.

--

B. Urban