manage values in a stack

src/gc.c

@@ -475,7 +475,7 @@ gc_mark_object(pic_state *pic, struct pic_object *obj)
   }
   case PIC_TT_VAR: {
     struct pic_var *var = (struct pic_var *)obj;
-    gc_mark(pic, var->value);
+    gc_mark(pic, var->stack);
     break;
   }
   case PIC_TT_IREP: {

src/var.c

@@ -3,21 +3,31 @@
  */
 
 #include "picrin.h"
-#include "picrin/proc.h"
 #include "picrin/var.h"
+#include "picrin/pair.h"
 
 static pic_value
 var_ref(pic_state *pic, struct pic_var *var)
 {
-  UNUSED(pic);
-  return var->value;
+  return pic_car(pic, var->stack);
 }
 
 static void
 var_set(pic_state *pic, struct pic_var *var, pic_value value)
 {
-  UNUSED(pic);
-  var->value = value;
+  pic_set_car(pic, var->stack, value);
+}
+
+static void
+var_push(pic_state *pic, struct pic_var *var, pic_value value)
+{
+  var->stack = pic_cons(pic, value, var->stack);
+}
+
+static void
+var_pop(pic_state *pic, struct pic_var *var)
+{
+  var->stack = pic_cdr(pic, var->stack);
 }
 
 struct pic_var *
@@ -26,7 +36,9 @@ pic_var_new(pic_state *pic, pic_value init)
   struct pic_var *var;
 
   var = (struct pic_var *)pic_obj_alloc(pic, sizeof(struct pic_var), PIC_TT_VAR);
-  var->value = init;
+  var->stack = pic_nil_value();
+
+  var_push(pic, var, init);
 
   return var;
 }
@@ -61,6 +73,36 @@ pic_var_set(pic_state *pic, const char *name, pic_value value)
   var_set(pic, var, value);
 }
 
+void
+pic_var_push(pic_state *pic, const char *name, pic_value value)
+{
+  pic_value v;
+  struct pic_var *var;
+
+  v = pic_ref(pic, name);
+
+  pic_assert_type(pic, v, var);
+
+  var = pic_var_ptr(v);
+
+  var_push(pic, var, value);
+}
+
+void
+pic_var_pop(pic_state *pic, const char *name)
+{
+  pic_value v;
+  struct pic_var *var;
+
+  v = pic_ref(pic, name);
+
+  pic_assert_type(pic, v, var);
+
+  var = pic_var_ptr(v);
+
+  var_pop(pic, var);
+}
+
 static pic_value
 pic_var_make_var(pic_state *pic)
 {
@@ -98,7 +140,36 @@ pic_var_var_set(pic_state *pic)
 
   var = pic_var_ptr(v);
   var_set(pic, var, val);
+  return pic_none_value();
+}
 
+static pic_value
+pic_var_var_push(pic_state *pic)
+{
+  struct pic_var *var;
+  pic_value v, val;
+
+  pic_get_args(pic, "oo", &v, &val);
+
+  pic_assert_type(pic, v, var);
+
+  var = pic_var_ptr(v);
+  var_push(pic, var, val);
+  return pic_none_value();
+}
+
+static pic_value
+pic_var_var_pop(pic_state *pic)
+{
+  struct pic_var *var;
+  pic_value v;
+
+  pic_get_args(pic, "o", &v);
+
+  pic_assert_type(pic, v, var);
+
+  var = pic_var_ptr(v);
+  var_pop(pic, var);
   return pic_none_value();
 }
 
@@ -109,5 +180,7 @@ pic_init_var(pic_state *pic)
     pic_defun(pic, "make-var", pic_var_make_var);
     pic_defun(pic, "var-ref", pic_var_var_ref);
     pic_defun(pic, "var-set!", pic_var_var_set);
+    pic_defun(pic, "var-push!", pic_var_var_push);
+    pic_defun(pic, "var-pop!", pic_var_var_pop);
   }
 }