Use DefaultFunction in RelativePosition

- since the default value for Position is Nowhere now.
Also, remove reduntant header and change stream to ostream in to_strings

libwccl/ops/functions/position/relativeposition.cpp

@@ -7,10 +7,9 @@ namespace Wccl {
 RelativePosition::BaseRetValPtr RelativePosition::apply_internal(
 	const FunExecContext &context) const
 {
-	static const Constant<Position> nowhere((Position(Position::Nowhere)));
 	const RetValPtr& orig_pos = pos_expr_->apply(context);
 	if(orig_pos->get_value() == Position::Nowhere) {
-		return nowhere.apply(context);
+		return detail::DefaultFunction<Position>()->apply(context);
 	}
 	const SentenceContext& sc = context.sentence_context();
 	return RetValPtr(new Position(offset_ + sc.get_rel_position(*orig_pos)));
@@ -18,7 +17,7 @@ RelativePosition::BaseRetValPtr RelativePosition::apply_internal(
 
 std::string RelativePosition::to_string(const Corpus2::Tagset &tagset) const
 {
-	std::stringstream ss;
+	std::ostringstream ss;
 	ss << pos_expr_->to_string(tagset);
 	if(offset_ >= 0) {
 		ss << " + " << offset_;
@@ -30,7 +29,7 @@ std::string RelativePosition::to_string(const Corpus2::Tagset &tagset) const
 
 std::string RelativePosition::to_raw_string() const
 {
-	std::stringstream ss;
+	std::ostringstream ss;
 	ss << pos_expr_->to_raw_string();
 	if(offset_ >= 0) {
 		ss << " + " << offset_;

libwccl/ops/functions/position/relativeposition.h

@@ -2,7 +2,6 @@
 #define LIBWCCL_OPS_FUNCTIONS_POSITION_RELATIVEPOSITION_H
 
 #include <libwccl/ops/function.h>
-#include <libwccl/ops/formatters.h>
 #include <libwccl/values/position.h>
 
 namespace Wccl {