add string type

include/picrin/port.h

@@ -1,8 +1,6 @@
 #ifndef PORT_H__
 #define PORT_H__
 
-#include "picrin.h"
-
 enum pic_port_flag {
   PIC_PORT_IN,
   PIC_PORT_OUT,

include/picrin/string.h

@@ -0,0 +1,14 @@
+#ifndef STRING_H__
+#define STRING_H__
+
+struct pic_string {
+  PIC_OBJECT_HEADER
+  const char *str;
+  size_t len;
+};
+
+#define pic_str_ptr(v) ((struct pic_string *)v.u.data)
+
+pic_value pic_str_new_cstr(pic_state *, const char *);
+
+#endif

include/picrin/value.h

@@ -28,7 +28,8 @@ enum pic_tt {
   PIC_TT_PAIR,
   PIC_TT_SYMBOL,
   PIC_TT_PROC,
-  PIC_TT_PORT
+  PIC_TT_PORT,
+  PIC_TT_STRING
 };
 
 #define PIC_OBJECT_HEADER			\