Utilities for debugging Proto expression trees Pretty-print a Proto expression tree. A PolymorphicFunctionObject which accepts a Proto expression tree and pretty-prints it to an ostream for debugging purposes. void void Expr const & std::ostream &std::cout The ostream to which the expression tree will be written. int 0 The starting indentation depth for this node. Children nodes will be displayed at a starting depth of depth+4. void Expr const & The Proto expression tree to pretty-print std::ostream & The ostream to which the output should be written. If not specified, defaults to std::cout. void Expr const & Pretty-print a Proto expression tree. Equivalent to proto::functional::display_expr(0, sout)(expr).