diff --git a/MY-BASIC Quick Reference.pdf b/MY-BASIC Quick Reference.pdf
index b6ea452..dd40d65 100644
Binary files a/MY-BASIC Quick Reference.pdf and b/MY-BASIC Quick Reference.pdf differ
diff --git a/clean.cmd b/clean.cmd
index 94f85dd..47a6939 100644
--- a/clean.cmd
+++ b/clean.cmd
@@ -13,6 +13,7 @@ del /f /s /q *.obj
 del /f /s /q *.pdb
 del /f /s /q *.sdf
 del /f /s /q *.suo
+del /f /s /q *.user
 del /f /s /q *.vc.db
 
 del /f /s /q output\*.dep
diff --git a/core/my_basic.c b/core/my_basic.c
index 7baa70e..1ced6d7 100755
--- a/core/my_basic.c
+++ b/core/my_basic.c
@@ -3253,7 +3253,7 @@ static int mb_uu_getbom(const char** ch) {
 }
 
 #ifdef MB_ENABLE_UNICODE
-/* Determine whether a buffer is a UTF8 encoded character, and return taken bytes */
+/* Determine whether a buffer starts with a UTF8 encoded character, and return taken byte count */
 static int mb_uu_ischar(const char* ch) {
 	/* Copyright 2008, 2009 Bjoern Hoehrmann, http://bjoern.hoehrmann.de/utf-8/decoder/dfa/ */
 #	define _TAKE(__ch, __c, __r) do { __c = *__ch++; __r++; } while(0)
@@ -4827,7 +4827,7 @@ static bool_t _is_operator_char(char c) {
 	);
 }
 
-/* Determine whether a character is a exponential char */
+/* Determine whether a character is exponential char */
 static bool_t _is_exponential_char(char c) {
 	return (c == 'e') || (c == 'E');
 }
@@ -7383,9 +7383,9 @@ static _ls_node_t* _node_at_list(_list_t* coll, int index) {
 	_fill_ranged(coll);
 
 	if(index >= 0 && index < (int)coll->count) {
-		/* Layout: HEAD ... LEFT ... PIVOT ... RIGHT ... TAIL
+		/* Position: HEAD ... LEFT ... PIVOT ... RIGHT ... TAIL
+			PIVOT is a cached node and,
 			LEN(HEAD to LEFT) == LEN(LEFT to PIVOT) && LEN(PIVOT to RIGHT) == LEN(RIGHT to TAIL)
-			PIVOT is a cached node
 		 */
 		int head = 0,
 			left = coll->cached_index / 2,
@@ -12261,7 +12261,7 @@ int mb_get_class_userdata(struct mb_interpreter_t* s, void** l, void** d) {
 #ifdef MB_ENABLE_CLASS
 	int result = MB_FUNC_OK;
 
-	if(!s || !l || !d) {
+	if(!s || !d) {
 		result = MB_FUNC_ERR;
 
 		goto _exit;
@@ -12295,7 +12295,7 @@ int mb_set_class_userdata(struct mb_interpreter_t* s, void** l, void* d) {
 #ifdef MB_ENABLE_CLASS
 	int result = MB_FUNC_OK;
 
-	if(!s || !l || !d) {
+	if(!s || !d) {
 		result = MB_FUNC_ERR;
 
 		goto _exit;
@@ -12323,8 +12323,9 @@ int mb_get_value_by_name(struct mb_interpreter_t* s, void** l, const char* n, mb
 	int result = MB_FUNC_OK;
 	_ls_node_t* tmp = 0;
 	_object_t* obj = 0;
+	mb_unrefvar(l);
 
-	if(!s || !l || !n) {
+	if(!s || !n) {
 		result = MB_FUNC_ERR;
 
 		goto _exit;
@@ -12350,7 +12351,7 @@ int mb_add_var(struct mb_interpreter_t* s, void** l, const char* n, mb_value_t v
 	_var_t* var = 0;
 	_ls_node_t* tmp = 0;
 
-	if(!s || !l || !n) {
+	if(!s || !n) {
 		result = MB_FUNC_ERR;
 
 		goto _exit;
diff --git a/core/my_basic.h b/core/my_basic.h
index a256582..2947968 100755
--- a/core/my_basic.h
+++ b/core/my_basic.h
@@ -352,7 +352,7 @@ extern "C" {
 #	define MB_LOOP_BREAK 101
 #	define MB_LOOP_CONTINUE 102
 #	define MB_SUB_RETURN 103
-#	define MB_EXTENDED_ABORT 1001
+#	define MB_EXTENDED_ABORT 201
 #endif /* MB_CODES */
 
 #ifndef mb_check
@@ -570,7 +570,7 @@ typedef int (* mb_has_routine_arg_func_t)(struct mb_interpreter_t*, void**, mb_v
 typedef int (* mb_pop_routine_arg_func_t)(struct mb_interpreter_t*, void**, mb_value_t*, unsigned, unsigned*, void*, mb_value_t*);
 typedef int (* mb_routine_func_t)(struct mb_interpreter_t*, void**, mb_value_t*, unsigned, void*, mb_has_routine_arg_func_t, mb_pop_routine_arg_func_t);
 typedef int (* mb_debug_stepped_handler_t)(struct mb_interpreter_t*, void**, char*, int, unsigned short, unsigned short);
-typedef void (* mb_error_handler_t)(struct mb_interpreter_t*, enum mb_error_e, char*, char*, int, unsigned short, unsigned short, int);
+typedef void (* mb_error_handler_t)(struct mb_interpreter_t*, mb_error_e, char*, char*, int, unsigned short, unsigned short, int);
 typedef int (* mb_print_func_t)(const char*, ...);
 typedef int (* mb_input_func_t)(char*, int);
 typedef int (* mb_import_handler_t)(struct mb_interpreter_t*, const char*);
diff --git a/sample/sample07.bas b/sample/sample07.bas
index 457a5c1..33b3f66 100644
--- a/sample/sample07.bas
+++ b/sample/sample07.bas
@@ -92,7 +92,7 @@ enddef
 
 ' This is a brainfuck interpreter written with MY-BASIC
 input "Input: ", cmd$
-' Use a sample code?
+' Input "hello" to use hello-world
 if cmd$ = "hello" then
 	cmd$ = "++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+++.>++.<<+++++++++++++++.>.+++.------.--------.>+.>."
 endif
diff --git a/sample/yard/entity.bas b/sample/yard/entity.bas
index eaf1ed7..9cb5129 100644
--- a/sample/yard/entity.bas
+++ b/sample/yard/entity.bas
@@ -3,7 +3,7 @@
 ' Copyright (C) 2011 - 2017 Wang Renxin. All rights reserved.
 ' For more information about MY-BASIC, see https://github.com/paladin-t/my_basic/
 
-Class entity
+class entity
 	var name = ""
 
 	var alive = true
diff --git a/shell/main.c b/shell/main.c
index d17651c..f924128 100755
--- a/shell/main.c
+++ b/shell/main.c
@@ -101,9 +101,9 @@ extern "C" {
 
 static struct mb_interpreter_t* bas = 0;
 
-static jmp_buf _mem_failure_point;
+static jmp_buf mem_failure_point;
 
-#define _CHECK_MEM(__p) do { if(!(__p)) { longjmp(_mem_failure_point, 1); } } while(0)
+#define _CHECK_MEM(__p) do { if(!(__p)) { longjmp(mem_failure_point, 1); } } while(0)
 
 /* ========================================================} */
 
@@ -185,8 +185,8 @@ static long alloc_bytes = 0;
 static long in_pool_count = 0;
 static long in_pool_bytes = 0;
 
-static long _POOL_THRESHOLD_COUNT = 0;
-static long _POOL_THRESHOLD_BYTES = 1024 * 1024 * 32;
+static long POOL_THRESHOLD_COUNT = 0;
+static long POOL_THRESHOLD_BYTES = 1024 * 1024 * 32;
 
 #define _POOL_NODE_ALLOC(size) (((char*)malloc(sizeof(_pool_tag_t) + size)) + sizeof(_pool_tag_t))
 #define _POOL_NODE_PTR(s) (s - sizeof(_pool_tag_t))
@@ -211,10 +211,10 @@ static void _tidy_mem_pool(bool_t force) {
 	char* s = 0;
 
 	if(!force) {
-		if(_POOL_THRESHOLD_COUNT > 0 && in_pool_count < _POOL_THRESHOLD_COUNT)
+		if(POOL_THRESHOLD_COUNT > 0 && in_pool_count < POOL_THRESHOLD_COUNT)
 			return;
 
-		if(_POOL_THRESHOLD_BYTES > 0 && in_pool_bytes < _POOL_THRESHOLD_BYTES)
+		if(POOL_THRESHOLD_BYTES > 0 && in_pool_bytes < POOL_THRESHOLD_BYTES)
 			return;
 	}
 
@@ -1193,7 +1193,7 @@ static bool_t _process_parameters(int argc, char* argv[]) {
 
 #if _USE_MEM_POOL
 	if(memp)
-		_POOL_THRESHOLD_BYTES = atoi(memp);
+		POOL_THRESHOLD_BYTES = atoi(memp);
 #else /* _USE_MEM_POOL */
 	mb_unrefvar(memp);
 #endif /* _USE_MEM_POOL */
@@ -1224,12 +1224,12 @@ static bool_t _process_parameters(int argc, char* argv[]) {
 #	define _OS "IOS"
 #elif defined MB_OS_MAC
 #	define _OS "MACOS"
-#elif defined MB_OS_UNIX
-#	define _OS "UNIX"
-#elif defined MB_OS_LINUX
-#	define _OS "LINUX"
 #elif defined MB_OS_ANDROID
 #	define _OS "ANDROID"
+#elif defined MB_OS_LINUX
+#	define _OS "LINUX"
+#elif defined MB_OS_UNIX
+#	define _OS "UNIX"
 #else
 #	define _OS "UNKNOWN"
 #endif /* MB_OS_WIN */
@@ -1569,7 +1569,7 @@ int main(int argc, char* argv[]) {
 
 	atexit(_on_exit);
 
-	if(setjmp(_mem_failure_point)) {
+	if(setjmp(mem_failure_point)) {
 		_printf("Error: out of memory.\n");
 
 		exit(1);