Dear list,
  I have a couple of questions, I started to play with FFI, so these
are newbie ones, my intention is to port the ZOOM library. I was there
happily writing ExternalStructure's until I found one that kills the
VM. Then I've realized I have some basic doubts about FFI:

1) I have this C struct

    odr Struct Reference
    ===============
        int 	direction
        int 	error
        unsigned char * 	buf
        int 	top
        int 	size
        int 	pos
        const unsigned char * 	bp
        NMEM 	mem
        struct Odr_private * 	op

which I wrote (with a lot of brilliant inspiration) like:

ZOOMODR class>> fields
	"  self defineFields  "
	^ #(
		(direction  'long')
		(error      'long')
		(buf        'char *')
		(top         'long')
		(size        'long')
		(pos         'long')
		(bp          'char *')
		(mem       'ZOOMNMem')
		(odrPrivate 'void *')  " ========= HERE ========= "
	)

I don't know if this exists, the HERE means : I want to avoid to write
an external structure for this...

        Odr_private Struct Reference
        =====================
            struct odr_constack * 	stack_first
            struct odr_constack * 	stack_top
            const char ** 	tmp_names_buf
            int 	tmp_names_sz
            struct Odr_ber_tag 	odr_ber_tag
            yaz_iconv_t 	iconv_handle
            int 	error_id
            char 	element [80]
            void(* 	stream_write )(ODR o, void *handle, int type,
const char *buf, int len)
            void(* 	stream_close )(void *handle)
            int 	can_grow
            int 	t_class
            int 	t_tag
            int 	enable_bias
            int 	choice_bias
            int 	lenlen
            FILE * 	print
            int 	indent

After a look at the fields, I supose I do not care about the contents
of that struct. It is ok the

... (odrPrivate 'void *') ...

magic line to "stop" these C structs?
If not, is there a way to say "I don't care what follows from here"
(i.e. pass automagically nil to that pointer) ?

2)
    Z_NamePlusRecord Struct Reference
    =================================
    Z_DatabaseName * 	databaseName
    int 	which
    union {
       Z_External *   databaseRecord
       Z_DiagRec *   surrogateDiagnostic
       Z_FragmentSyntax *   startingFragment
       Z_FragmentSyntax *   intermediateFragment
       Z_FragmentSyntax *   finalFragment
    }	u

Is there something special to do about an union in the #fields method?

Thanks in advance.

Hernán