Re: [tcltk-perl] Drop listify [PATCH]

[Gisle A. <gi...@Ac...>]

"Jeff Hobbs" <je...@Ac...> writes:

> > Is there a semantic difference between [list a b c] and {a b c}
> > in Tcl the language?  If not, then I don't think they should be
> > different when passed to perl either.
> 
> OH man, oh man ... this is sticky.  Yes and no.  At the C level,
> the first is a pure list (perl AV), while the second is just a
> string.  You can stringify the list and listify the string, just
> as you can convert an SvPV to an AV and back.

I read this answer to mean that there is no semantic difference.  What
it is represented as internally should not matter.  There is no two-way
conversion between strings and arrays in perl.

>                                              The trick is that
> in passing a Tcl_Obj to become and SV, I check the object types
> first for efficient conversion (trying to reduce round-tripping
> through strings, which I think you've noticed the positive
> effect of).

I understand all that, but I don't think this should dictate the
semantics.

> I think that I've properly handled it with the recent changes to
> call and icall.  If something is still "not right", please tell
> me.

To me it wrong if:

    $tcl->Eval("set var {a b c}");

returns something different to perl than

    $tcl->Eval("set var [list a b c]");

if these two expressions have exactly the same semantics in Tcl.

I would suggest that we always return the string in scalar context and
always list in list context.  If the value is not a valid list, then
we croak in list context.

Alternatively we return return some object that just wraps the Tcl_Obj
and can used as both a string and array reference.  This can be
combined with the previous alternative, so this only happens in scalar
context.

Alternatively we have a separate methods that indicate if a string,
array reference or list is wanted as return value.

   $tcl->Eval_giving_string($code);
   $tcl->Eval_giving_arrayref($code);
   $tcl->Eval_giving_list($code);

--Gisle