[Boost-users] library planed for expression evaluation?

Hello, does some plans for an library for expression evaluation exist? The user should be able to define its own operators (unary and binary with priority/affinity) and operands. The user can then store a sequence of its operators and operands in a vector in infix order. A special function creates from the vector an expression tree and evaluates the tree (calling the implemented action of each operator/operand -> the action can depend of the subsequent/child operators). With regards, Oliver