diff --git a/README_ZH.md b/README_ZH.md
index 95de5c9..ebff9e6 100644
--- a/README_ZH.md
+++ b/README_ZH.md
@@ -20,7 +20,7 @@
 | [(liii os)](goldfish/liii/os.scm) | 库类似于 Python 的 `os` 模块 | `getenv`, `mkdir` |
 | [(liii uuid)](goldfish/liii/uuid.scm) | UUID 生成 | `uuid4` |
 | [(liii sys)](goldfish/liii/sys.scm) | 库类似于 Python 的 `sys` 模块 | `argv` |
-| [(liii error)](goldfish/liii/error.scm) | 提供类似Python的错误函数 | `error-os`函数抛出`'os-error`，类似Python的OSError |
+| [(liii error)](goldfish/liii/error.scm) | 提供类似Python的错误函数 | `os-error`函数抛出`'os-error`，类似Python的OSError |
 | [(liii check)](goldfish/liii/check.scm) | 基于SRFI 78的轻量级测试库加强版 | `check`, `check-catch` | 
 
 ### SRFI
diff --git a/goldfish/liii/error.scm b/goldfish/liii/error.scm
index 468dd80..616f016 100644
--- a/goldfish/liii/error.scm
+++ b/goldfish/liii/error.scm
@@ -14,23 +14,37 @@
 ; under the License.
 ;
 
+; see https://docs.python.org/3/library/exceptions.html#exception-hierarchy
+
 (define-library (liii error)
-(export error-file-not-found error-os error-not-a-directory
-  error-file-exists)
+(export ???
+  os-error file-not-found-error not-a-directory-error file-exists-error
+  timeout-error
+  type-error value-error)
 (import (scheme process-context))
 (begin
 
-(define (error-file-not-found msg)
-  (error 'file-not-found-error msg))
-
-(define (error-os msg)
+(define (os-error msg)
   (error 'os-error msg))
 
-(define (error-not-a-directory msg)
+(define (file-not-found-error msg)
+  (error 'file-not-found-error msg))
+
+(define (not-a-directory-error msg)
   (error 'not-a-directory-error msg))
 
-(define (error-file-exists msg)
+(define (file-exists-error msg)
   (error 'file-exists-error msg))
 
+(define (timeout-error args)
+  (apply (cons 'timeout-error args) error))
+
+(define (type-error args)
+  (apply (cons 'type-error args) error))
+
+; nice Scala style to throw the not-implemented-error
+(define (???)
+  (error 'not-implemented-error))
+
 ) ; begin
 ) ; define-library
diff --git a/goldfish/liii/os.scm b/goldfish/liii/os.scm
index e64652c..0d992fe 100644
--- a/goldfish/liii/os.scm
+++ b/goldfish/liii/os.scm
@@ -48,10 +48,10 @@
 
 (define (%check-dir-andthen path f)
   (cond ((not (file-exists? path))
-         (error-file-not-found
+         (file-not-found-error
            (string-append "No such file or directory: '" path "'")))
         ((not (isdir path))
-         (error-not-a-directory
+         (not-a-directory-error
            (string-append "Not a directory: '" path "'")))
         (else (f path))))
 
@@ -60,7 +60,7 @@
 
 (define (mkdir path)
   (if (file-exists? path)
-    (error-file-exists (string-append "File exists: '" path "'"))
+    (file-exists-error (string-append "File exists: '" path "'"))
     (g_mkdir path)))
 
 (define (rmdir path)
diff --git a/goldfish/liii/string.scm b/goldfish/liii/string.scm
new file mode 100644
index 0000000..33ed080
--- /dev/null
+++ b/goldfish/liii/string.scm
@@ -0,0 +1,35 @@
+;
+; Copyright (C) 2024 The Goldfish Scheme Authors
+;
+; Licensed under the Apache License, Version 2.0 (the "License");
+; you may not use this file except in compliance with the License.
+; You may obtain a copy of the License at
+;
+; http://www.apache.org/licenses/LICENSE-2.0
+;
+; Unless required by applicable law or agreed to in writing, software
+; distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+; WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+; License for the specific language governing permissions and limitations
+; under the License.
+;
+
+(define-library (liii string)
+(export
+  string-null? string-copy string-join
+  string-every string-any
+  string-take string-take-right string-drop string-drop-right
+  string-pad string-pad-right
+  string-trim string-trim-right string-trim-both
+  string-prefix? string-suffix?
+  string-index string-index-right
+  string-contains string-count
+  string-reverse
+  string-tokenize
+)
+(import (srfi srfi-13)
+        (srfi srfi-1)
+        (liii error))
+(begin
+) ; end of begin
+) ; end of library
diff --git a/tests/liii/error-test.scm b/tests/liii/error-test.scm
new file mode 100644
index 0000000..7ed6dec
--- /dev/null
+++ b/tests/liii/error-test.scm
@@ -0,0 +1,22 @@
+;
+; Copyright (C) 2024 The Goldfish Scheme Authors
+;
+; Licensed under the Apache License, Version 2.0 (the "License");
+; you may not use this file except in compliance with the License.
+; You may obtain a copy of the License at
+;
+; http://www.apache.org/licenses/LICENSE-2.0
+;
+; Unless required by applicable law or agreed to in writing, software
+; distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+; WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+; License for the specific language governing permissions and limitations
+; under the License.
+;
+
+(import (liii check)
+        (liii error))
+
+(check-catch 'not-implemented-error (lambda () (???)))
+
+(check-report)
diff --git a/tests/liii/string-test.scm b/tests/liii/string-test.scm
new file mode 100644
index 0000000..8f7a348
--- /dev/null
+++ b/tests/liii/string-test.scm
@@ -0,0 +1,23 @@
+;
+; Copyright (C) 2024 The Goldfish Scheme Authors
+;
+; Licensed under the Apache License, Version 2.0 (the "License");
+; you may not use this file except in compliance with the License.
+; You may obtain a copy of the License at
+;
+; http://www.apache.org/licenses/LICENSE-2.0
+;
+; Unless required by applicable law or agreed to in writing, software
+; distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+; WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+; License for the specific language governing permissions and limitations
+; under the License.
+;
+
+(import (liii check)
+        (liii error))
+
+(check (mk-string " " (list 1 2 3)) => "1 2 3")
+(check (mk-string " " (list )) => "")
+
+(check-report)
diff --git a/tests/scheme/process-context-test.scm b/tests/scheme/process-context-test.scm
index da4da8f..ede2ca3 100644
--- a/tests/scheme/process-context-test.scm
+++ b/tests/scheme/process-context-test.scm
@@ -15,9 +15,15 @@
 ;
 
 (import (srfi srfi-78)
-        (scheme process-context))
+        (scheme process-context)
+        (srfi srfi-13)
+        (liii os))
 
 (check-set-mode! 'report-failed)
 
 ; (check (get-environment-variable "USER") => "da")
-; (check (get-environment-variable "HOME") => "/home/da")
+(when (os-linux?)
+  (check (string-prefix? "/home" (get-environment-variable "HOME"))
+         => #t))
+
+(check-report)