6 files changed, 32 insertions, 4 deletions

diff --git a/builtin.cpp b/builtin.cpp
index 6eb0c0f..b983167 100644
--- a/builtin.cpp
+++ b/builtin.cpp
@@ -954,7 +954,10 @@ BUILTIN_PROC_DEF(pair_set_car) {
     ARGS_EXACTLY_TWO;
     if (!args->car->is_pair_obj())
         throw TokenError("pair", RUN_ERR_WRONG_TYPE);
-    TO_PAIR(args->car)->car = TO_PAIR(args->cdr)->car;
+    Pair *p = TO_PAIR(args->car);
+    gc.expose(p->car);
+    p->car = TO_PAIR(args->cdr)->car;
+    gc.attach(p->car);
     return unspec_obj;
 }
 
@@ -962,7 +965,10 @@ BUILTIN_PROC_DEF(pair_set_cdr) {
     ARGS_EXACTLY_TWO;
     if (!args->car->is_pair_obj())
         throw TokenError("pair", RUN_ERR_WRONG_TYPE);
-    TO_PAIR(args->car)->cdr = TO_PAIR(args->cdr)->car;
+    Pair *p = TO_PAIR(args->car);
+    gc.expose(p->cdr);
+    p->cdr = TO_PAIR(args->cdr)->car;
+    gc.attach(p->cdr);
     return unspec_obj;
 }
 
diff --git a/model.cpp b/model.cpp
index cb3d5c6..416c583 100644
--- a/model.cpp
+++ b/model.cpp
@@ -27,6 +27,10 @@ bool FrameObj::is_parse_bracket() {
 
 EvalObj::EvalObj(int _otype) : FrameObj(CLS_EVAL_OBJ), otype(_otype) {}
 
+bool EvalObj::is_container() {
+    return otype & CLS_CONTAINER;
+}
+
 void EvalObj::prepare(Pair *pc) {}
 
 bool EvalObj::is_simple_obj() {
diff --git a/model.h b/model.h
index 1ace1c9..9ccdf20 100644
--- a/model.h
+++ b/model.h
@@ -92,6 +92,7 @@ class EvalObj : public FrameObj {
         bool is_prom_obj();
         /** Check if the object is a vector */
         bool is_vect_obj();
+        bool is_container();
         int get_otype();
         virtual void prepare(Pair *pc);
         /** Any EvalObj has its external representation */
@@ -106,6 +107,8 @@ class Container: public EvalObj {
     public:
     size_t gc_refs;
     Container(int otype);
+    virtual void gc_decrement() = 0;
+    virtual void gc_trigger(EvalObj ** &tail) = 0;
 };
 
 /** @class RetAddr
diff --git a/parser.cpp b/parser.cpp
index c53ec14..a8577d3 100644
--- a/parser.cpp
+++ b/parser.cpp
@@ -190,7 +190,9 @@ Pair *ASTGenerator::absorb(Tokenizor *tk) {
                         TO_PAIR(lst)->cdr != empty_list)
                         throw NormalError(PAR_ERR_IMPROPER_PAIR);
                     improper = true;
-                    lst = TO_PAIR(lst)->car;
+                    Pair *_lst = TO_PAIR(lst);
+                    lst = _lst->car;
+                    delete _lst;
                 }
                 else
                 {
diff --git a/types.cpp b/types.cpp
index 7988c59..edeeb99 100644
--- a/types.cpp
+++ b/types.cpp
@@ -27,11 +27,22 @@ Pair::~Pair() {
     gc.expose(cdr);
 }
 
+void Pair::gc_decrement() {
+    if (car->is_container())
+        static_cast<Container*>(car)->gc_refs--;
+    if (cdr->is_container())
+        static_cast<Container*>(cdr)->gc_refs--;
+}
+
+void Pair::gc_trigger(EvalObj ** &tail) {
+    *tail++ = car;
+    *tail++ = cdr;
+}
+
 ReprCons *Pair::get_repr_cons() {
     return new PairReprCons(this, this);
 }
 
-
 ParseBracket::ParseBracket(unsigned char _btype) :
     FrameObj(CLS_SIM_OBJ | CLS_PAR_BRA), btype(_btype) {}
 
diff --git a/types.h b/types.h
index 93dac66..f76a0cc 100644
--- a/types.h
+++ b/types.h
@@ -53,6 +53,8 @@ class Pair : public Container {/*{{{*/
         Pair(EvalObj *car, EvalObj *cdr);  /**< Create a Pair (car . cdr) */
         ~Pair();
         ReprCons *get_repr_cons();
+        void gc_decrement();
+        void gc_trigger(EvalObj ** &tail);
 };/*}}}*/
 
 /** @class EmptyList