No longer destroy the list of free variables.

It so happens that this list will tell us which variables
need to be captured.

12/definition.cpp

@@ -114,15 +114,13 @@ void definition_group::find_free(type_mgr& mgr, type_env_ptr& env, std::set<std:
 
     for(auto& def_pair : defs_defn) {
         def_pair.second->find_free(mgr, env);
-        std::set<std::string> local_dependencies;
         for(auto& free_var : def_pair.second->free_variables) {
             if(defs_defn.find(free_var) == defs_defn.end()) {
                 into.insert(free_var);
             } else {
-                local_dependencies.insert(free_var);
+                def_pair.second->nearby_variables.insert(free_var);
             }
         }
-        std::swap(def_pair.second->free_variables, local_dependencies);
     }
 }
 
@@ -140,7 +138,7 @@ void definition_group::typecheck(type_mgr& mgr) {
         def_defn.second->find_free(mgr, env);
         dependency_graph.add_function(def_defn.second->name);
 
-        for(auto& dependency : def_defn.second->free_variables) {
+        for(auto& dependency : def_defn.second->nearby_variables) {
             if(defs_defn.find(dependency) == defs_defn.end())
                 throw 0;
             dependency_graph.add_edge(def_defn.second->name, dependency);

12/definition.hpp

@@ -30,6 +30,7 @@ struct definition_defn {
     type_env_ptr env;
     type_env_ptr var_env;
     std::set<std::string> free_variables;
+    std::set<std::string> nearby_variables;
     type_ptr full_type;
     type_ptr return_type;