diff --git a/include/picrin/port.h b/include/picrin/port.h
index 6ae638f2..914680f3 100644
--- a/include/picrin/port.h
+++ b/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,
diff --git a/include/picrin/string.h b/include/picrin/string.h
new file mode 100644
index 00000000..ccef6efb
--- /dev/null
+++ b/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
diff --git a/include/picrin/value.h b/include/picrin/value.h
index c6ade674..212466e0 100644
--- a/include/picrin/value.h
+++ b/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			\
diff --git a/src/gc.c b/src/gc.c
index 4884c3b3..b1530f62 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -4,6 +4,7 @@
 #include "picrin/gc.h"
 #include "picrin/irep.h"
 #include "picrin/proc.h"
+#include "picrin/string.h"
 
 #if GC_DEBUG
 # include <stdio.h>
@@ -148,7 +149,15 @@ gc_mark_object(pic_state *pic, struct pic_object *obj)
   case PIC_TT_PROC: {
     break;
   }
-  default:
+  case PIC_TT_PORT: {
+    break;
+  }
+  case PIC_TT_STRING: {
+  }
+  case PIC_TT_NIL:
+  case PIC_TT_BOOL:
+  case PIC_TT_FLOAT:
+  case PIC_TT_UNDEF:
     pic_abort(pic, "logic flaw");
   }
 }
@@ -233,16 +242,16 @@ gc_finalize_object(pic_state *pic, struct pic_object *obj)
     break;
   }
   case PIC_TT_PROC: {
-    struct pic_proc *proc;
-
-    proc = (struct pic_proc *)obj;
-
-    /* free irep */
-    pic_free(pic, proc->u.irep->code);
-    pic_free(pic, proc->u.irep);
     break;
   }
-  default:
+  case PIC_TT_STRING: {
+    pic_free(pic, (void*)((struct pic_string *)obj)->str);
+    break;
+  }
+  case PIC_TT_NIL:
+  case PIC_TT_BOOL:
+  case PIC_TT_FLOAT:
+  case PIC_TT_UNDEF:
     pic_abort(pic, "logic flaw");
   }
 }
diff --git a/src/port.c b/src/port.c
index bf502534..32dfd8fc 100644
--- a/src/port.c
+++ b/src/port.c
@@ -4,6 +4,7 @@
 #include "picrin.h"
 #include "picrin/proc.h"
 #include "picrin/port.h"
+#include "picrin/string.h"
 
 static void write_pair(pic_state *pic, struct pic_pair *pair);
 
@@ -40,6 +41,9 @@ write(pic_state *pic, pic_value obj)
   case PIC_TT_PORT:
     printf("#<port %p>", pic_port_ptr(obj));
     break;
+  case PIC_TT_STRING:
+    printf("\"%s\"", pic_str_ptr(obj)->str);
+    break;
   }
 }
 
diff --git a/src/string.c b/src/string.c
new file mode 100644
index 00000000..14b6850c
--- /dev/null
+++ b/src/string.c
@@ -0,0 +1,22 @@
+#include <string.h>
+
+#include "picrin.h"
+#include "picrin/string.h"
+
+pic_value
+pic_str_new_cstr(pic_state *pic, const char *cstr)
+{
+  struct pic_string *str;
+  size_t len;
+  char *new_str;
+
+  len = strlen(cstr);
+  new_str = (char *)pic_alloc(pic, len + 1);
+  strncpy(new_str, cstr, len + 1);
+
+  str = (struct pic_string *)pic_obj_alloc(pic, sizeof(struct pic_string), PIC_TT_STRING);
+  str->len = len;
+  str->str = new_str;
+
+  return pic_obj_value(str);
+}