decide value representation

include/picrin.h

@@ -1,6 +1,8 @@
 #ifndef PICRIN_H__
 #define PICRIN_H__
 
+#include "picrin/value.h"
+
 typedef struct {
 } pic_state;
 

include/picrin/value.h

@@ -0,0 +1,38 @@
+#ifndef VALUE_H__
+#define VALUE_H__
+
+enum pic_vtype {
+  PIC_VTYPE_HEAP
+};
+
+typedef struct {
+  enum pic_vtype type;
+  union {
+    void *data;
+  } u;
+} pic_value;
+
+enum pic_tt {
+  PIC_TT_PAIR,
+  PIC_TT_SYMBOL
+};
+
+#define PIC_OBJECT_HEADER			\
+  enum pic_tt tt;
+
+struct pic_object {
+  PIC_OBJECT_HEADER
+};
+
+struct pic_pair {
+  PIC_OBJECT_HEADER
+  pic_value car;
+  pic_value cdr;
+};
+
+struct pic_symbol {
+  PIC_OBJECT_HEADER
+  char *name;
+};
+
+#endif