Hi Thomas,

...

Trying to mimic what comes in the Lazy Vector example

http://www.boost.org/doc/libs/1_45_0/doc/html/proto/users_guide.html#boost_p... <snip>

The type EmtDomain is incomplete when it is used in EmtExpr (proto::extends ...).

So is also lazy_vector_domain when it is used in lazy_vector_expr. What's different here? (See below.)

The solution is to forward declare EmtExpr, define the Domain and then define the expression wrapper.

Thanks, that works. :) But, I do still wonder why the same order of definition for Lazy Vector didn't work here: Grammar > Forward Declaration of Domain > (Context) > Expression Wrapper > Domain Do you mind shedding light on this too? TIA, --Hossein