diff --git a/extlib/benz/codegen.c b/extlib/benz/codegen.c
index 51df8c0c..987124d2 100644
--- a/extlib/benz/codegen.c
+++ b/extlib/benz/codegen.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/opcode.h"
 
 /**
  * macro expander
diff --git a/extlib/benz/include/picrin/irep.h b/extlib/benz/include/picrin/irep.h
index bcaf4eb6..aa230848 100644
--- a/extlib/benz/include/picrin/irep.h
+++ b/extlib/benz/include/picrin/irep.h
@@ -9,49 +9,8 @@
 extern "C" {
 #endif
 
-enum pic_opcode {
-  OP_NOP,
-  OP_POP,
-  OP_PUSHUNDEF,
-  OP_PUSHNIL,
-  OP_PUSHTRUE,
-  OP_PUSHFALSE,
-  OP_PUSHINT,
-  OP_PUSHCHAR,
-  OP_PUSHCONST,
-  OP_GREF,
-  OP_GSET,
-  OP_LREF,
-  OP_LSET,
-  OP_CREF,
-  OP_CSET,
-  OP_JMP,
-  OP_JMPIF,
-  OP_NOT,
-  OP_CALL,
-  OP_TAILCALL,
-  OP_RET,
-  OP_LAMBDA,
-  OP_CONS,
-  OP_CAR,
-  OP_CDR,
-  OP_NILP,
-  OP_SYMBOLP,
-  OP_PAIRP,
-  OP_ADD,
-  OP_SUB,
-  OP_MUL,
-  OP_DIV,
-  OP_EQ,
-  OP_LT,
-  OP_LE,
-  OP_GT,
-  OP_GE,
-  OP_STOP
-};
-
 typedef struct {
-  enum pic_opcode insn;
+  int insn;
   union {
     int i;
     char c;
@@ -62,11 +21,6 @@ typedef struct {
   } u;
 } pic_code;
 
-#define PIC_INIT_CODE_I(code, op, ival) do {    \
-    code.insn = op;                             \
-    code.u.i = ival;                            \
-  } while (0)
-
 struct pic_irep {
   PIC_OBJECT_HEADER
   pic_code *code;
@@ -82,149 +36,6 @@ pic_value pic_expand(pic_state *, pic_value, struct pic_env *);
 pic_value pic_analyze(pic_state *, pic_value);
 struct pic_irep *pic_codegen(pic_state *, pic_value);
 
-#if DEBUG
-
-PIC_INLINE void
-pic_dump_code(pic_code c)
-{
-  printf("[%2d] ", c.insn);
-  switch (c.insn) {
-  case OP_NOP:
-    puts("OP_NOP");
-    break;
-  case OP_POP:
-    puts("OP_POP");
-    break;
-  case OP_PUSHUNDEF:
-    puts("OP_PUSHUNDEF");
-    break;
-  case OP_PUSHNIL:
-    puts("OP_PUSHNIL");
-    break;
-  case OP_PUSHTRUE:
-    puts("OP_PUSHTRUE");
-    break;
-  case OP_PUSHFALSE:
-    puts("OP_PUSHFALSE");
-    break;
-  case OP_PUSHINT:
-    printf("OP_PUSHINT\t%d\n", c.u.i);
-    break;
-  case OP_PUSHCHAR:
-    printf("OP_PUSHCHAR\t%c\n", c.u.c);
-    break;
-  case OP_PUSHCONST:
-    printf("OP_PUSHCONST\t%d\n", c.u.i);
-    break;
-  case OP_GREF:
-    printf("OP_GREF\t%i\n", c.u.i);
-    break;
-  case OP_GSET:
-    printf("OP_GSET\t%i\n", c.u.i);
-    break;
-  case OP_LREF:
-    printf("OP_LREF\t%d\n", c.u.i);
-    break;
-  case OP_LSET:
-    printf("OP_LSET\t%d\n", c.u.i);
-    break;
-  case OP_CREF:
-    printf("OP_CREF\t%d\t%d\n", c.u.r.depth, c.u.r.idx);
-    break;
-  case OP_CSET:
-    printf("OP_CSET\t%d\t%d\n", c.u.r.depth, c.u.r.idx);
-    break;
-  case OP_JMP:
-    printf("OP_JMP\t%x\n", c.u.i);
-    break;
-  case OP_JMPIF:
-    printf("OP_JMPIF\t%x\n", c.u.i);
-    break;
-  case OP_NOT:
-    puts("OP_NOT");
-    break;
-  case OP_CALL:
-    printf("OP_CALL\t%d\n", c.u.i);
-    break;
-  case OP_TAILCALL:
-    printf("OP_TAILCALL\t%d\n", c.u.i);
-    break;
-  case OP_RET:
-    puts("OP_RET");
-    break;
-  case OP_LAMBDA:
-    printf("OP_LAMBDA\t%d\n", c.u.i);
-    break;
-  case OP_CONS:
-    puts("OP_CONS");
-    break;
-  case OP_CAR:
-    puts("OP_CAR");
-    break;
-  case OP_NILP:
-    puts("OP_NILP");
-    break;
-  case OP_SYMBOLP:
-    puts("OP_SYMBOLP");
-    break;
-  case OP_PAIRP:
-    puts("OP_PAIRP");
-    break;
-  case OP_CDR:
-    puts("OP_CDR");
-    break;
-  case OP_ADD:
-    puts("OP_ADD");
-    break;
-  case OP_SUB:
-    puts("OP_SUB");
-    break;
-  case OP_MUL:
-    puts("OP_MUL");
-    break;
-  case OP_DIV:
-    puts("OP_DIV");
-    break;
-  case OP_EQ:
-    puts("OP_EQ");
-    break;
-  case OP_LT:
-    puts("OP_LT");
-    break;
-  case OP_LE:
-    puts("OP_LE");
-    break;
-  case OP_GT:
-    puts("OP_GT");
-    break;
-  case OP_GE:
-    puts("OP_GE");
-    break;
-  case OP_STOP:
-    puts("OP_STOP");
-    break;
-  }
-}
-
-PIC_INLINE void
-pic_dump_irep(struct pic_irep *irep)
-{
-  unsigned i;
-
-  printf("## irep %p\n", (void *)irep);
-  printf("[clen = %zd, argc = %d, localc = %d, capturec = %d]\n", irep->clen, irep->argc, irep->localc, irep->capturec);
-  for (i = 0; i < irep->clen; ++i) {
-    printf("%02x ", i);
-    pic_dump_code(irep->code[i]);
-  }
-
-  for (i = 0; i < irep->ilen; ++i) {
-    pic_dump_irep(irep->irep[i]);
-  }
-}
-
-#endif
-
 #if defined(__cplusplus)
 }
 #endif
diff --git a/extlib/benz/include/picrin/opcode.h b/extlib/benz/include/picrin/opcode.h
new file mode 100644
index 00000000..e3eb00a7
--- /dev/null
+++ b/extlib/benz/include/picrin/opcode.h
@@ -0,0 +1,205 @@
+/**
+ * See Copyright Notice in picrin.h
+ */
+
+#ifndef PICRIN_OPCODE_H
+#define PICRIN_OPCODE_H
+
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
+enum pic_opcode {
+  OP_NOP,
+  OP_POP,
+  OP_PUSHUNDEF,
+  OP_PUSHNIL,
+  OP_PUSHTRUE,
+  OP_PUSHFALSE,
+  OP_PUSHINT,
+  OP_PUSHCHAR,
+  OP_PUSHCONST,
+  OP_GREF,
+  OP_GSET,
+  OP_LREF,
+  OP_LSET,
+  OP_CREF,
+  OP_CSET,
+  OP_JMP,
+  OP_JMPIF,
+  OP_NOT,
+  OP_CALL,
+  OP_TAILCALL,
+  OP_RET,
+  OP_LAMBDA,
+  OP_CONS,
+  OP_CAR,
+  OP_CDR,
+  OP_NILP,
+  OP_SYMBOLP,
+  OP_PAIRP,
+  OP_ADD,
+  OP_SUB,
+  OP_MUL,
+  OP_DIV,
+  OP_EQ,
+  OP_LT,
+  OP_LE,
+  OP_GT,
+  OP_GE,
+  OP_STOP
+};
+
+#define PIC_INIT_CODE_I(code, op, ival) do {    \
+    code.insn = op;                             \
+    code.u.i = ival;                            \
+  } while (0)
+
+#if DEBUG
+
+PIC_INLINE void
+pic_dump_code(pic_code c)
+{
+  printf("[%2d] ", c.insn);
+  switch (c.insn) {
+  case OP_NOP:
+    puts("OP_NOP");
+    break;
+  case OP_POP:
+    puts("OP_POP");
+    break;
+  case OP_PUSHUNDEF:
+    puts("OP_PUSHUNDEF");
+    break;
+  case OP_PUSHNIL:
+    puts("OP_PUSHNIL");
+    break;
+  case OP_PUSHTRUE:
+    puts("OP_PUSHTRUE");
+    break;
+  case OP_PUSHFALSE:
+    puts("OP_PUSHFALSE");
+    break;
+  case OP_PUSHINT:
+    printf("OP_PUSHINT\t%d\n", c.u.i);
+    break;
+  case OP_PUSHCHAR:
+    printf("OP_PUSHCHAR\t%c\n", c.u.c);
+    break;
+  case OP_PUSHCONST:
+    printf("OP_PUSHCONST\t%d\n", c.u.i);
+    break;
+  case OP_GREF:
+    printf("OP_GREF\t%i\n", c.u.i);
+    break;
+  case OP_GSET:
+    printf("OP_GSET\t%i\n", c.u.i);
+    break;
+  case OP_LREF:
+    printf("OP_LREF\t%d\n", c.u.i);
+    break;
+  case OP_LSET:
+    printf("OP_LSET\t%d\n", c.u.i);
+    break;
+  case OP_CREF:
+    printf("OP_CREF\t%d\t%d\n", c.u.r.depth, c.u.r.idx);
+    break;
+  case OP_CSET:
+    printf("OP_CSET\t%d\t%d\n", c.u.r.depth, c.u.r.idx);
+    break;
+  case OP_JMP:
+    printf("OP_JMP\t%x\n", c.u.i);
+    break;
+  case OP_JMPIF:
+    printf("OP_JMPIF\t%x\n", c.u.i);
+    break;
+  case OP_NOT:
+    puts("OP_NOT");
+    break;
+  case OP_CALL:
+    printf("OP_CALL\t%d\n", c.u.i);
+    break;
+  case OP_TAILCALL:
+    printf("OP_TAILCALL\t%d\n", c.u.i);
+    break;
+  case OP_RET:
+    puts("OP_RET");
+    break;
+  case OP_LAMBDA:
+    printf("OP_LAMBDA\t%d\n", c.u.i);
+    break;
+  case OP_CONS:
+    puts("OP_CONS");
+    break;
+  case OP_CAR:
+    puts("OP_CAR");
+    break;
+  case OP_NILP:
+    puts("OP_NILP");
+    break;
+  case OP_SYMBOLP:
+    puts("OP_SYMBOLP");
+    break;
+  case OP_PAIRP:
+    puts("OP_PAIRP");
+    break;
+  case OP_CDR:
+    puts("OP_CDR");
+    break;
+  case OP_ADD:
+    puts("OP_ADD");
+    break;
+  case OP_SUB:
+    puts("OP_SUB");
+    break;
+  case OP_MUL:
+    puts("OP_MUL");
+    break;
+  case OP_DIV:
+    puts("OP_DIV");
+    break;
+  case OP_EQ:
+    puts("OP_EQ");
+    break;
+  case OP_LT:
+    puts("OP_LT");
+    break;
+  case OP_LE:
+    puts("OP_LE");
+    break;
+  case OP_GT:
+    puts("OP_GT");
+    break;
+  case OP_GE:
+    puts("OP_GE");
+    break;
+  case OP_STOP:
+    puts("OP_STOP");
+    break;
+  }
+}
+
+PIC_INLINE void
+pic_dump_irep(struct pic_irep *irep)
+{
+  unsigned i;
+
+  printf("## irep %p\n", (void *)irep);
+  printf("[clen = %zd, argc = %d, localc = %d, capturec = %d]\n", irep->clen, irep->argc, irep->localc, irep->capturec);
+  for (i = 0; i < irep->clen; ++i) {
+    printf("%02x ", i);
+    pic_dump_code(irep->code[i]);
+  }
+
+  for (i = 0; i < irep->ilen; ++i) {
+    pic_dump_irep(irep->irep[i]);
+  }
+}
+
+#endif
+
+#if defined(__cplusplus)
+}
+#endif
+
+#endif
diff --git a/extlib/benz/vm.c b/extlib/benz/vm.c
index ec63da8b..dd719d24 100644
--- a/extlib/benz/vm.c
+++ b/extlib/benz/vm.c
@@ -3,6 +3,7 @@
  */
 
 #include "picrin.h"
+#include "picrin/opcode.h"
 
 #define GET_OPERAND(pic,n) ((pic)->ci->fp[(n)])