diff --git a/contrib/10.optional/CMakeLists.txt b/contrib/10.optional/CMakeLists.txt
new file mode 100644
index 00000000..c6a60a8a
--- /dev/null
+++ b/contrib/10.optional/CMakeLists.txt
@@ -0,0 +1,9 @@
+file(GLOB OPTIONAL_FILES ${PROJECT_SOURCE_DIR}/contrib/10.optional/piclib/*.scm)
+list(APPEND PICLIB_CONTRIB_LIBS ${OPTIONAL_FILES})
+add_custom_target(test-optional
+  for test in ${PROJECT_SOURCE_DIR}/contrib/10.optional/t/*.scm \;
+  do
+    bin/picrin "$$test" \;
+  done
+  DEPENDS repl)
+set(CONTRIB_TESTS ${CONTRIB_TESTS} test-optional)
diff --git a/contrib/10.optional/piclib/optional.scm b/contrib/10.optional/piclib/optional.scm
new file mode 100644
index 00000000..362f7fe0
--- /dev/null
+++ b/contrib/10.optional/piclib/optional.scm
@@ -0,0 +1,24 @@
+(define-library (picrin optional)
+  (import (scheme base))
+
+  (define-syntax optional
+    (syntax-rules ()
+      ((_ args default)
+       (let ((t args))
+         (if (null? t) default (car t))))))
+
+  (define-syntax let-optionals*
+    (syntax-rules ()
+      ((_ args () body ...)
+       (begin body ...))
+      ((_ args ((var default) . tail) body ...)
+       (let* ((t args)
+              (var (if (null? t) default (car t)))
+              (remain (if (null? t) '() (cdr t))))
+         (let-optionals* remain tail body ...)))
+      ((_ args rest body ...)
+       (let ((rest args))
+         body ...))))
+
+  (export optional
+          let-optionals*))
diff --git a/contrib/10.optional/t/test.scm b/contrib/10.optional/t/test.scm
new file mode 100644
index 00000000..5ac0b45c
--- /dev/null
+++ b/contrib/10.optional/t/test.scm
@@ -0,0 +1,15 @@
+(import (scheme base)
+        (picrin optional)
+        (picrin test))
+
+(test 0 (optional '() 0))
+(test 1 (optional '(1) 0))
+
+(test '(0 0) (let-optionals* '() ((a 0) (b 0)) (list a b)))
+(test '(1 0) (let-optionals* '(1) ((a 0) (b 0)) (list a b)))
+(test '(1 2) (let-optionals* '(1 2) ((a 0) (b 0)) (list a b)))
+(test '(1 1) (let-optionals* '(1) ((a 0) (b a)) (list a b)))
+
+(test '(0 ()) (let-optionals* '() ((a 0) . r) (list a r)))
+(test '(1 ()) (let-optionals* '(1) ((a 0) . r) (list a r)))
+(test '(1 (2)) (let-optionals* '(1 2) ((a 0) . r) (list a r)))
diff --git a/contrib/20.repl/CMakeLists.txt b/contrib/20.repl/CMakeLists.txt
index c0a24065..7fc3bf06 100644
--- a/contrib/20.repl/CMakeLists.txt
+++ b/contrib/20.repl/CMakeLists.txt
@@ -1 +1,3 @@
 list(APPEND PICLIB_CONTRIB_LIBS ${PROJECT_SOURCE_DIR}/contrib/20.repl/repl.scm)
+list(APPEND PICRIN_CONTRIB_SOURCES ${PROJECT_SOURCE_DIR}/contrib/20.repl/repl.c)
+list(APPEND PICRIN_CONTRIB_INITS repl)
diff --git a/contrib/20.repl/repl.c b/contrib/20.repl/repl.c
new file mode 100644
index 00000000..1398a202
--- /dev/null
+++ b/contrib/20.repl/repl.c
@@ -0,0 +1,21 @@
+#include "picrin.h"
+
+#include <unistd.h>
+
+
+static pic_value
+pic_repl_tty_p(pic_state *pic)
+{
+
+  pic_get_args(pic, "");
+
+  return pic_bool_value((isatty(STDIN_FILENO)));
+}
+
+void
+pic_init_repl(pic_state *pic)
+{
+  pic_deflibrary (pic, "(picrin repl)") {
+    pic_defun(pic, "tty?", pic_repl_tty_p);
+  }
+}
diff --git a/contrib/20.repl/repl.scm b/contrib/20.repl/repl.scm
index 2b9d4812..bed94d0e 100644
--- a/contrib/20.repl/repl.scm
+++ b/contrib/20.repl/repl.scm
@@ -11,7 +11,7 @@
    (else
     (begin
       (define (readline str)
-        (display str)
+        (if (tty?) (display str))
         (read-line))
       (define (add-history str)
         #f))))
diff --git a/extlib/benz b/extlib/benz
index a22eef10..15889a5f 160000
--- a/extlib/benz
+++ b/extlib/benz
@@ -1 +1 @@
-Subproject commit a22eef106077850db7dd2d9da5703a4d0b3b9ffe
+Subproject commit 15889a5feb515bd67ee7dc2c6419d16703151a54