On Thu, Aug 02, 2007 at 11:58:57AM +0200, Mauricio Fernandez wrote:
> On Thu, Aug 02, 2007 at 11:20:50AM +0200, Mauricio Fernandez wrote:
> > > It looks like we are really close. The next (final?) issue is that we have a
> > > function with signature
> > > 
> > >     val eval : kpp -> string -> value list -> value list
> > > 
> > > where
> > > 
> > >     type value =
> > > 	| Vstr of string
> > > 	| Vtup of value list
> > > 
> > > which we want to export to Ruby. We tried:
> > > 
> > >     Interface.generate(EXT_NAME) do
> > >       value = sym_variant("value") do |t|
> > > 	non_constant :Vstr, STRING
> > > 	non_constant :Vtup, LIST(t)
> > >       end
> > [...]
> > > but it doesn't work (it segfaults inside the extension).
> > > 
> > > How does one represent `value' on the Ruby side?
> > 
> > I think you have to wrap the LIST(t) in a TUPLE():
> > 
> >   value = sym_variant("value") do |t|
> >    non_constant :Vstr, STRING
> >    non_constant :Vtup, TUPLE(LIST(t))
> >   end
> > 
> > I'll try to either auto-detect this or perform a compile-time check.
> 
> Ignore that; I forgot that rocaml already detects when such extra boxing is
> needed and performs it automatically, so   non_constant :Vtup, LIST(foo)
> should work already. It can't be due to the type being recursive either
> because that works fine in the tree example. 
 
Thanks. We ended up doing

    Interface.generate(EXT_NAME) do
      kpp_value_t = sym_variant("kpp_value_t") do |t|
	non_constant :Vstr, STRING
	non_constant :Vtup, LIST(t)
      end

      def_class("KPP") do |c|
	t = c.abstract_type
	ctxt = LIST(kpp_value_t)
	fun "make", STRING => t
	method "eval", [t, STRING, ctxt] => ctxt
	...
      end
    end

so we can say

    kpp.eval("", [[:Vstr, "woot!"]])

> Just to make sure, are you calling  eval as in
> 
>   kpp.eval(str, [[[ :Vtup, [ [[:Vstr, "foo"]] ] ]]])
>                 
> The outer pair of [ ] because it's a block, the next one because it holds a
> LIST, then the block represented as [symbol, value] where value is a block
> holding a list of [symbol, value] blocks.
> 
> If you've got the wrong number of [ ], maybe the generated extension isn't
> detecting it, and hence the crash.
> 		       
> Yes, it's hard to get the above right, so I'll see if something can be done
> from Ruby to make it easier.

That would be nice. Thanks for the explanation Mauricio.

And thanks to everybody responding on this thread - it looks like we are all
set now.

-- 
Jos Backus
jos at catnook.com