hook concat into stl

src/str.rs

@@ -43,7 +43,7 @@ pub fn get_echo() -> Function {
                         Ctr::Seg(c)     => string.push_str(ast_as_string(c.clone(), true).as_str()),
                         Ctr::None       => ()
                     }
-                    println!(string)
+                    println!("{}", string);
                     return true;
                 }) {
                     eprintln!("circuit loop in echo should not have returned false")