Re: [Boost-users] Creating new operators & function under proto

Joel FALCOU wrote:

Hi,

I tried follwoing the tutorial to create new functions to use in Proto but it failed. Let's say I want to have a new unary function called worker that create an expression that ought to be matched by the following grammar :

struct worker_grammar : or_< terminal< user_func<_> >, function< worker_tag, terminal< user_func<_> > > {}; I keep getting a 'no type named proto_expr_base in worker_tag' error.

Right, because unless "worker_tag" is a proto expression or a proto grammar, it cannot be a parameter to proto::function<>. The grammar function will match a binary expression with tag::function and where the first child matches A and the second child matches B. You might get a little farther with something like this: terminal::type const worker = {{}}; Now you can say: worker('a') and it will generate an expression that matches the grammar: function, _>

Related question, how can I make a new function which tag is a tempalte class whose tempalte parameter is used to change how the associated transform is performed, I tried : <snip>

If, for example, worker_tag were a template, you might instead do something like .... template typename proto::result_of::make_expr< proto::tag::function ,worker_tag<Tag> ,Arg

::type worker(Arg const &arg) { return proto::make_exprproto::tag::function(worker_tag<Tag>(), arg); }

The resulting expression would match the grammar: function >, _> HTH, -- Eric Niebler BoostPro Computing http://www.boostpro.com