going to try the queue approach

include/blt/gp/typesystem.h

@@ -38,6 +38,9 @@ namespace blt::gp
     struct type_id : integer_type<u64>
     {
         using integer_type::integer_type;
+
+        // debug helper.
+        [[nodiscard]] std::string name(gp_program& program) const;
     };
 
     class type

src/tree.cpp

@@ -836,7 +836,8 @@ namespace blt::gp
                             continue;
                         if (type == other_point_info.argument_types[i])
                         {
-                            BLT_TRACE("Consuming other type {} at index {} ", type, index);
+                            BLT_TRACE("Consuming other type {} (aka {}) at index {} replacing {} (aka {})", type, type.name(*tree->m_program), index,
+                                      i, storage.our_current_types[i].name(*tree->m_program));
                             consumed = true;
                             const auto s1 = storage.other_children[index].size();
                             const auto s2 = storage.our_children[i].size();
@@ -869,7 +870,8 @@ namespace blt::gp
                             continue;
                         if (type == point_info.argument_types[i])
                         {
-                            BLT_TRACE("Consuming our type {} at index {} ", type, index);
+                            BLT_TRACE("Consuming other type {} (aka {}) at index {} replacing {} (aka {})", type, type.name(*tree->m_program), index,
+                                      i, storage.other_current_types[i].name(*tree->m_program));
                             consumed = true;
                             const auto s1 = storage.our_children[index].size();
                             const auto s2 = storage.other_children[i].size();
@@ -895,10 +897,16 @@ namespace blt::gp
 
 #if BLT_DEBUG_LEVEL >= 1
             for (const auto& [i, a, b] : in_pairs(storage.our_current_types, other_point_info.argument_types).enumerate().take(common_size).flatten())
-                BLT_ASSERT_MSG(a == b, ("[Our] Mismatched types at index " + std::to_string(i) + " expected '" + std::string(tree->m_program->get_typesystem().get_type(a).name()) + "' but found '" +
+                BLT_ASSERT_MSG(
+                a == b,
+                ("[Our] Mismatched types at index " + std::to_string(i) + " expected '" + std::string(tree->m_program->get_typesystem().get_type(a).
+                        name()) + "' but found '" +
                     std::string(tree->m_program->get_typesystem().get_type(b).name()) + "'").c_str());
             for (const auto& [i, a, b] : in_pairs(storage.other_current_types, point_info.argument_types).enumerate().take(common_size).flatten())
-                BLT_ASSERT_MSG(a == b, ("[Other] Mismatched types at index " + std::to_string(i) + " expected '" + std::string(tree->m_program->get_typesystem().get_type(a).name()) + "' but found '" +
+                BLT_ASSERT_MSG(
+                a == b,
+                ("[Other] Mismatched types at index " + std::to_string(i) + " expected '" + std::string(tree->m_program->get_typesystem().get_type(a).
+                        name()) + "' but found '" +
                     std::string(tree->m_program->get_typesystem().get_type(b).name()) + "'").c_str());
 #endif
 
@@ -913,7 +921,7 @@ namespace blt::gp
                         continue;
                     if (type == point_info.argument_types[i])
                     {
-                        // BLT_TRACE("[Our] Consuming type {} at index {} being inserted into {}", type, index, insert_index);
+                        BLT_TRACE("[Our] Consuming type {} at index {} being inserted into {}", type, index, insert_index);
                         storage.temp.clear(*tree->m_program);
                         copy_subtree(storage.our_children[i], storage.temp);
                         insert_index = other_tree.manipulate().easy_manipulator().insert_subtree(subtree_point_t{insert_index}, storage.temp);
@@ -941,7 +949,7 @@ namespace blt::gp
                         continue;
                     if (type == other_point_info.argument_types[i])
                     {
-                        // BLT_TRACE("[Other] Consuming type {} at index {} being inserted into {}", type, index, insert_index);
+                        BLT_TRACE("[Other] Consuming type {} at index {} being inserted into {}", type, index, insert_index);
                         storage.temp.clear(*tree->m_program);
                         other_tree.manipulate().easy_manipulator().copy_subtree(storage.other_children[i], storage.temp);
                         insert_index = insert_subtree(subtree_point_t{insert_index}, storage.temp);

src/typesystem.cpp

@@ -16,8 +16,12 @@
  *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 #include <blt/gp/typesystem.h>
+#include <blt/gp/program.h>
 
 namespace blt::gp
 {
-
+    std::string type_id::name(gp_program& program) const
+    {
+        return std::string(program.get_typesystem().get_type(id).name());
+    }
 }