From b284973035a71e9b25d0fb8d3323ba0a84b05144 Mon Sep 17 00:00:00 2001
From: Yuichi Nishiwaki <yuichi.nishiwaki@gmail.com>
Date: Sat, 12 Oct 2013 14:40:01 +0900
Subject: [PATCH] add #<undef>

---
 include/picrin/value.h |  3 +++
 src/value.c            | 12 ++++++++++++
 src/vm.c               |  5 +++++
 src/write.c            |  3 +++
 4 files changed, 23 insertions(+)

diff --git a/include/picrin/value.h b/include/picrin/value.h
index d155674b..3666aec1 100644
--- a/include/picrin/value.h
+++ b/include/picrin/value.h
@@ -4,6 +4,7 @@
 enum pic_vtype {
   PIC_VTYPE_NIL,
   PIC_VTYPE_INT,
+  PIC_VTYPE_UNDEF,
   PIC_VTYPE_HEAP
 };
 
@@ -19,6 +20,7 @@ enum pic_tt {
   /* immediate */
   PIC_TT_NIL,
   PIC_TT_INT,
+  PIC_TT_UNDEF,
   /* heap */
   PIC_TT_PAIR,
   PIC_TT_SYMBOL
@@ -48,6 +50,7 @@ struct pic_symbol {
 enum pic_tt pic_type(pic_value);
 
 pic_value pic_nil_value();
+pic_value pic_undef_value();
 pic_value pic_obj_value(void *);
 pic_value pic_int_value(int);
 
diff --git a/src/value.c b/src/value.c
index 7c5c6acc..2233fb95 100644
--- a/src/value.c
+++ b/src/value.c
@@ -8,6 +8,8 @@ pic_type(pic_value v)
     return PIC_TT_NIL;
   case PIC_VTYPE_INT:
     return PIC_TT_INT;
+  case PIC_VTYPE_UNDEF:
+    return PIC_TT_UNDEF;
   case PIC_VTYPE_HEAP:
     return ((struct pic_object *)v.u.data)->tt;
   }
@@ -42,3 +44,13 @@ pic_int_value(int i)
   v.u.i = i;
   return v;
 }
+
+pic_value
+pic_undef_value()
+{
+  pic_value v;
+
+  v.type = PIC_VTYPE_UNDEF;
+  v.u.data = NULL;
+  return v;
+}
diff --git a/src/vm.c b/src/vm.c
index d8f514b7..f669fd84 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -5,6 +5,7 @@
 enum pic_instruction {
   OP_PUSHNIL,
   OP_PUSHI,
+  OP_PUSHUNDEF,
   OP_CONS,
   OP_ADD,
   OP_STOP
@@ -114,6 +115,10 @@ pic_run(pic_state *pic, struct pic_proc *proc, pic_value args)
       *++sp = pic_int_value(pc->u.i);
       break;
     }
+    case OP_PUSHUNDEF: {
+      *++sp = pic_undef_value();
+      break;
+    }
     case OP_CONS: {
       pic_value a, b;
       a = *sp--;
diff --git a/src/write.c b/src/write.c
index c920e455..c0705711 100644
--- a/src/write.c
+++ b/src/write.c
@@ -23,5 +23,8 @@ pic_debug(pic_state *pic, pic_value obj)
   case PIC_TT_INT:
     printf("%d", pic_int(obj));
     break;
+  case PIC_TT_UNDEF:
+    printf("#<undef>");
+    break;
   }
 }