diff --git a/HISTORY b/HISTORY
index 4d2d0ec..428a33d 100755
--- a/HISTORY
+++ b/HISTORY
@@ -1,3 +1,6 @@
+Oct. 9 2017
+Improved expression evaluation speed
+
 Oct. 5 2017
 Fixed an infinity loop bug with error handling, thanks to Saar for pointing it out
 Fixed a wrong error locating bug, thanks to Saar for pointing it out
diff --git a/MY-BASIC Quick Reference.pdf b/MY-BASIC Quick Reference.pdf
index 784cded..bd94b97 100644
Binary files a/MY-BASIC Quick Reference.pdf and b/MY-BASIC Quick Reference.pdf differ
diff --git a/core/my_basic.c b/core/my_basic.c
index 2bcd963..9e80143 100755
--- a/core/my_basic.c
+++ b/core/my_basic.c
@@ -642,6 +642,9 @@ typedef struct _object_t {
 		_raw_t raw;
 	} data;
 	bool_t is_ref _PACK1;
+#ifdef MB_PREFER_SPEED
+	bool_t is_const _PACK1;
+#endif /* MB_PREFER_SPEED */
 #ifdef MB_ENABLE_SOURCE_TRACE
 	int source_pos;
 	unsigned short source_row;
@@ -3645,6 +3648,16 @@ static int _calc_expression(mb_interpreter_t* s, _ls_node_t** l, _object_t** val
 
 	running = s->running_context;
 	ast = *l;
+
+	c = (_object_t*)ast->data;
+#ifdef MB_PREFER_SPEED
+	if(c->is_const) {
+		ast = ast->next;
+
+		goto _fast;
+	}
+#endif /* MB_PREFER_SPEED */
+
 	optr = _ls_create();
 	opnd = _ls_create();
 
@@ -3654,7 +3667,6 @@ static int _calc_expression(mb_interpreter_t* s, _ls_node_t** l, _object_t** val
 	*inep = 0;
 	_ls_pushback(s->in_neg_expr, inep);
 
-	c = (_object_t*)ast->data;
 	do {
 		if(c->type == _DT_STRING) {
 			if(ast->next) {
@@ -4045,6 +4057,22 @@ _var:
 	if(_is_unexpected_calc_type(s, c)) {
 		_handle_error_on_obj(s, SE_RN_INVALID_DATA_TYPE, s->source_file, DON(ast), MB_FUNC_ERR, _error, result);
 	}
+#ifdef MB_PREFER_SPEED
+	if(ast && ast->prev == *l) {
+		_object_t* obj = (_object_t*)(*l)->data;
+		switch(obj->type) {
+		case _DT_NIL: /* Fall through */
+		case _DT_INT: /* Fall through */
+		case _DT_REAL:
+			obj->is_const = true;
+
+			break;
+		default: /* Do nothing */
+			break;
+		}
+	}
+#endif /* MB_PREFER_SPEED */
+_fast:
 	if(c->type == _DT_VAR) {
 		(*val)->type = c->data.variable->data->type;
 		(*val)->data = c->data.variable->data->data;
@@ -4084,12 +4112,18 @@ _exit:
 		_LS_FOREACH(garbage, _destroy_object, _try_clear_intermediate_value, s);
 		_ls_destroy(garbage);
 	}
-	_ls_foreach(optr, _destroy_object_not_compile_time);
-	_ls_foreach(opnd, _destroy_object_not_compile_time);
-	_ls_destroy(optr);
-	_ls_destroy(opnd);
+	if(optr) {
+		_ls_foreach(optr, _destroy_object_not_compile_time);
+		_ls_destroy(optr);
+	}
+	if(opnd) {
+		_ls_foreach(opnd, _destroy_object_not_compile_time);
+		_ls_destroy(opnd);
+	}
+	if(inep) {
+		mb_free(_ls_popback(s->in_neg_expr));
+	}
 	*l = ast;
-	mb_free(_ls_popback(s->in_neg_expr));
 
 	return result;
 #undef _LAZY_INIT_GLIST
diff --git a/core/my_basic.h b/core/my_basic.h
index 76b6d32..22b964b 100755
--- a/core/my_basic.h
+++ b/core/my_basic.h
@@ -169,6 +169,10 @@ extern "C" {
 #	define MB_ENABLE_STACK_TRACE
 #endif /* MB_ENABLE_STACK_TRACE */
 
+#ifndef MB_ENABLE_FULL_ERROR
+#	define MB_ENABLE_FULL_ERROR
+#endif /* MB_ENABLE_FULL_ERROR */
+
 #ifndef MB_CONVERT_TO_INT_LEVEL_NONE
 #	define MB_CONVERT_TO_INT_LEVEL_NONE 0
 #endif /* MB_CONVERT_TO_INT_LEVEL_NONE */
@@ -180,9 +184,9 @@ extern "C" {
 #	define MB_CONVERT_TO_INT_LEVEL MB_CONVERT_TO_INT_LEVEL_ALL
 #endif /* MB_CONVERT_TO_INT_LEVEL */
 
-#ifndef MB_ENABLE_FULL_ERROR
-#	define MB_ENABLE_FULL_ERROR
-#endif /* MB_ENABLE_FULL_ERROR */
+#ifndef MB_PREFER_SPEED
+#	define MB_PREFER_SPEED
+#endif /* MB_PREFER_SPEED */
 
 #ifndef MB_COMPACT_MODE
 #	define MB_COMPACT_MODE
diff --git a/output/my_basic.exe b/output/my_basic.exe
index 20acbba..5ede9dc 100755
Binary files a/output/my_basic.exe and b/output/my_basic.exe differ
diff --git a/output/my_basic_mac b/output/my_basic_mac
index 3752ee1..d032e3b 100755
Binary files a/output/my_basic_mac and b/output/my_basic_mac differ