Refactor errors and update post draft.

13/definition.cpp

@@ -64,9 +64,9 @@ void definition_data::insert_constructors() const {
     type_ptr return_type(return_app);
     for(auto& var : vars) {
         if(var_set.find(var) != var_set.end())
-            throw std::runtime_error(
+            throw compiler_error(
                     std::string("type variable ") +
-                    var + std::string(" used twice in data type definition."));
+                    var + std::string(" used twice in data type definition."), loc);
         var_set.insert(var);
         return_app->arguments.push_back(type_ptr(new type_var(var)));
     }