[boost] [Proto] Expression as fusion/MPL sequence

Subject: [boost] [Proto] Expression as fusion/MPL sequence
From: Joel Falcou (joel.falcou_at_[hidden])
Date: 2011-06-01 20:02:43

Seems somethign crooky on this front. Calling fusion::at_c on expression 
ends up in error even after including boost/proto/fusion.hpp.
Same way, flatten used as a transform seems to not give me a type that 
can be passed to any fusion or mpl function. Looking at
proto/fusion.hpp I noticed that the iterator is indeed random_access but 
not the view itself which as a forward_traversal tag. Even
after fixing this, no dice, at_c<N>(some_proto_expr) still fails to compile.