diff --git a/README.md b/README.md
index ca361f1b..46e9e19a 100644
--- a/README.md
+++ b/README.md
@@ -74,6 +74,20 @@ Picrin is a lightweight scheme implementation intended to comply with full R7RS
         Sorting and Marging.
     
 
+## The REPL
+
+At the REPL start-up time, some usuful built-in libraries listed below will be automatically imported.
+
+- `(scheme base)`
+- `(scheme load)`
+- `(scheme process-context)`
+- `(scheme write)`
+- `(scheme file)`
+- `(scheme inexact)`
+- `(scheme cxr)`
+- `(scheme lazy)`
+- `(scheme time)`
+
 ## Compliance with R7RS
 
 | section | status | comments |
diff --git a/src/read.c b/src/read.c
index 4b0736b6..e768c10e 100644
--- a/src/read.c
+++ b/src/read.c
@@ -211,8 +211,7 @@ read_datum(int tok, yyscan_t scanner)
     error(NULL, scanner);
   }
 
-  /* unreachable */
-  return pic_undef_value();
+  UNREACHABLE();
 }
 
 static pic_value
diff --git a/tools/main.c b/tools/main.c
index ec44ec1f..2ef1a954 100644
--- a/tools/main.c
+++ b/tools/main.c
@@ -41,6 +41,15 @@ import_repllib(pic_state *pic)
   int ai = pic_gc_arena_preserve(pic);
 
   pic_import(pic, pic_read(pic, "(scheme base)"));
+  pic_import(pic, pic_read(pic, "(scheme load)"));
+  pic_import(pic, pic_read(pic, "(scheme process-context)"));
+  pic_import(pic, pic_read(pic, "(scheme write)"));
+  pic_import(pic, pic_read(pic, "(scheme file)"));
+  pic_import(pic, pic_read(pic, "(scheme inexact)"));
+  pic_import(pic, pic_read(pic, "(scheme cxr)"));
+  pic_import(pic, pic_read(pic, "(scheme lazy)"));
+  pic_import(pic, pic_read(pic, "(scheme time)"));
+  pic_import(pic, pic_read(pic, "(picrin macro)"));
 
 #if DEBUG
   puts("* imported repl libraries");