dcg-semicontext

As a follow up to this question which poses the problem Return count of items in a list but if two identical items are next to each other then don't increment the count. This code is the closest I came to solving this with DCG and semicontext. lookahead(C),[C] --> [C]. % empty list % No lookahead needed because last item in list. count_dcg(N,N) --> []. % single item in list % No lookahead needed because only one in list. count_dcg(N0,N) --> [_], \+ [_], { N is N0 + 1 }. % Lookahead needed because two items in list and % only want to remove first item. count_dcg(N0,N) --> [C1], lookahead(C2), {

This is a follow-on question from an earlier question from Mat's answer Starting with this e([number(0)] , t1 , Uc0 , Uc0, Bc0 , Bc0) --> []. e([number(1)] , t2 , Uc0 , Uc0, Bc0 , Bc0) --> []. e([number(2)] , t3 , Uc0 , Uc0, Bc0 , Bc0) --> []. e([op(neg),[Arg]] , u1(E) , [_|Uc0], Uc1, Bc0 , Bc1) --> [_], e(Arg , E , Uc0, Uc1, Bc0, Bc1). e([op(ln),[Arg]] , u2(E) , [_|Uc0], Uc1, Bc0 , Bc1) --> [_], e(Arg , E , Uc0, Uc1, Bc0, Bc1). e([op(add),[Left,Right]], b1(E0,E1) , Uc0 , Uc2, [_|Bc0], Bc2) --> [_,_], e(Left, E0, Uc0, Uc1, Bc0, Bc1), e(Right, E1, Uc1, Uc2, Bc1, Bc2). e([op(sub),[Left,Right]],

Consider the following extension to context-free grammars that permits rules to have in the left-hand side, one (or more) terminal on the right side of the non-terminal. That is, rules of the form: A b -> ... The right-hand side may be anything, like in context-free grammars. In particular, it is not required, that the right-hand side will have exactly the same terminal symbol at the end. In that case, this extension would be context-sensitive. But the terminal is not just a context. Sometimes, this terminal is called "pushback". Clearly, this is no longer CFG (type-2). It includes type-1. But