add variable export function

tests/test_lib_str.rs

@@ -1,11 +1,11 @@
 mod str_lib_tests {
     use relish::stdlib::{get_stdlib};
-    use relish::ast::{lex, eval, ast_to_string, VTable, FTable, Ctr};
+    use relish::ast::{lex, eval, VTable, FTable, Ctr};
     use std::rc::Rc;
     use std::cell::RefCell;
 
     #[test]
-    fn test_simple_echo() {
+    fn test_simple_concat() {
         let document = "(concat 'test')";
         let result = "test";
         let vt = Rc::new(RefCell::new(VTable::new()));
@@ -49,7 +49,7 @@ mod str_lib_tests {
     }
 
     #[test]
-    fn test_poly_echo() {
+    fn test_poly_concat() {
         let document = "(concat 'test' 1 2 3)";
         let result = "test123";
         let vt = Rc::new(RefCell::new(VTable::new()));
@@ -93,7 +93,7 @@ mod str_lib_tests {
     }
 
     #[test]
-    fn test_empty_echo() {
+    fn test_empty_concat() {
         let document = "(concat)";
         let result = "";
         let vt = Rc::new(RefCell::new(VTable::new()));