Hi, I am stilly trying o get my array computation DSEL up and running. The basic grammar is in place, what I am fighting with is protfying my literals. I.e. I have an array class, and I want the following expression: A(_i,_j) to become a function(literal<Array>(A), index_placeholder<0>, index_placeholder<1>) (simplified for readability, but the point should be clear). it works like this: proto::lit(A)(_i,_j) so how can I automate the turning of my array instance into a literal? I have access to the class definition and I tried subclassing terminal and literal and the PROTO_EXTENDS macro. The former two had no effect on my problem, and the latter didn't compile ( I tried various combindations of Expr and Derived parameters). Any ideas? Daniel