Hi, I am having a bit trouble with the semantic action of a sequential-or parser. Specifically my problem is with accessing the attribute of the sequential-or parser. My first observation is that the documentation at http://www.boost.org/doc/libs/1_41_0/libs/spirit/doc/html/spirit/qi/quick_re... defines the attribute type of (a || b) as tuple<A, B>. Unless I've misunderstood, this must be a typo as they should both be optional (it is never valid for both to be omitted but I would expect that client code be able to determine which out of (a), (b) or (a >> b) were provided.) My real problem is that applying a semantic action to [what I think is] an expression returning a sequential-or parser, results in the _1 referring to the attribute of the last parser on the right-hand-side of the sequential-or rather than the attribute of the sequential-or parser itself. In the following snippet (assume 'start' has an attribute of type S), idxspec = '[' >> (start || (':' >> -start)) [ _val = access_index (_r1,lvalue,_1) ] >> ']'; the function 'access_index' is called with an arg3 of type 'optional<S>' rather than the expected 'tuple<optional<S>, optional<optional<S>>>'. Wrapping the sequential-or expression in a 'repeat' directive as repeat(1)[start || (':' >> -start)] solved the problem but obviously gave me an unwanted sequence (albeit with only one element). The attribute type of the above came out to be vector<tuple<optional<S>, optional<optional<S>>>> as expected. To remove the sequence I created a parser directive called 'identity' following the form of 'repeat' which I have attached. My final rule is now idxspec = '[' >> identity[start || (':' >> -start)] [ _val = access_index (_r1,lvalue,_1) ] >> ']'; which is working fine; the _1 delivers an argument of type tuple<optional<S>, optional<optional<S>>> as required. However, I would have expected this behaviour from the first expression. Is this a a proto issue, a spirit issue or have I completely misunderstood something somewhere? It may or may not be relevant but I am using both spirit.classic and spirit 2.1 in the same file. This is historical and will be fixed in time but I guess it could be important. So far I have had no problems with the combination however. Additional info: I am using gcc 4.4.2, stlport 5.1.3 and boost 1.41.0. Regards, Adam