add pic_debug function

include/picrin.h

@@ -19,4 +19,6 @@ pic_value pic_cdr(pic_state *, pic_value);
 
 pic_value pic_intern_cstr(pic_state *, const char *);
 
+void pic_debug(pic_state *, pic_value);
+
 #endif

include/picrin/value.h

@@ -14,6 +14,9 @@ typedef struct {
 } pic_value;
 
 enum pic_tt {
+  /* immediate */
+  PIC_TT_NIL,
+  /* heap */
   PIC_TT_PAIR,
   PIC_TT_SYMBOL
 };
@@ -36,6 +39,11 @@ struct pic_symbol {
   char *name;
 };
 
+#define pic_pair_ptr(o) ((struct pic_pair *)o->u->data)
+#define pic_symbol_ptr(o) ((struct pic_symbol *)o->u->data)
+
+enum pic_tt pic_type(pic_value v);
+
 pic_value pic_nil_value();
 pic_value pic_obj_value(struct pic_object *obj);