diff --git a/include/picrin.h b/include/picrin.h
index 65eaed6c..320315e5 100644
--- a/include/picrin.h
+++ b/include/picrin.h
@@ -54,10 +54,6 @@ void pic_close(pic_state *);
 void pic_get_args(pic_state *, const char *, ...);
 void pic_defun(pic_state *, const char *, pic_func_t);
 
-pic_value pic_cons(pic_state *, pic_value, pic_value);
-pic_value pic_car(pic_state *, pic_value);
-pic_value pic_cdr(pic_state *, pic_value);
-
 bool pic_eq_p(pic_state *, pic_value, pic_value);
 
 pic_value pic_intern_cstr(pic_state *, const char *);
diff --git a/include/picrin/pair.h b/include/picrin/pair.h
new file mode 100644
index 00000000..53cabfc9
--- /dev/null
+++ b/include/picrin/pair.h
@@ -0,0 +1,12 @@
+#ifndef PAIR_H__
+#define PAIR_H__
+
+pic_value pic_cons(pic_state *, pic_value, pic_value);
+pic_value pic_car(pic_state *, pic_value);
+pic_value pic_cdr(pic_state *, pic_value);
+
+pic_value pic_list(pic_state *, size_t, ...);
+
+pic_value pic_assq(pic_state *, pic_value key, pic_value assoc);
+
+#endif
diff --git a/src/pair.c b/src/pair.c
index 18d6839e..d2a4003f 100644
--- a/src/pair.c
+++ b/src/pair.c
@@ -1,4 +1,5 @@
 #include "picrin.h"
+#include "picrin/pair.h"
 
 pic_value
 pic_cons(pic_state *pic, pic_value car, pic_value cdr)
@@ -31,3 +32,21 @@ pic_cdr(pic_state *pic, pic_value obj)
 
   return pair->cdr;
 }
+
+pic_value
+pic_assq(pic_state *pic, pic_value key, pic_value assoc)
+{
+  pic_value cell;
+
+ enter:
+
+  if (pic_nil_p(assoc))
+    return assoc;
+
+  cell = pic_car(pic, assoc);
+  if (pic_eq_p(pic, key, pic_car(pic, cell)))
+    return cell;
+
+  assoc = pic_cdr(pic, assoc);
+  goto enter;
+}
diff --git a/src/parse.y b/src/parse.y
index ca4ca611..8aaf0207 100644
--- a/src/parse.y
+++ b/src/parse.y
@@ -3,6 +3,7 @@
 #include <stdio.h>
 
 #include "picrin.h"
+#include "picrin/pair.h"
 
 #define YYERROR_VERBOSE 1
 
diff --git a/src/time.c b/src/time.c
index 3de5c44b..12f79f3d 100644
--- a/src/time.c
+++ b/src/time.c
@@ -1,5 +1,4 @@
 #include <time.h>
-#include <stdio.h>
 
 #include "picrin.h"
 
diff --git a/src/vm.c b/src/vm.c
index ee8513d5..e74b98e0 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -5,24 +5,7 @@
 #include "picrin.h"
 #include "picrin/irep.h"
 #include "picrin/proc.h"
-
-static pic_value
-pic_assq(pic_state *pic, pic_value key, pic_value assoc)
-{
-  pic_value cell;
-
- enter:
-
-  if (pic_nil_p(assoc))
-    return assoc;
-
-  cell = pic_car(pic, assoc);
-  if (pic_eq_p(pic, key, pic_car(pic, cell)))
-    return cell;
-
-  assoc = pic_cdr(pic, assoc);
-  goto enter;
-}
+#include "picrin/pair.h"
 
 static bool
 env_lookup(pic_state *pic, pic_value sym, struct pic_env *env, int *depth, int *idx)