finish eval referencing issues, update func tests

src/func.rs

@@ -152,7 +152,7 @@ pub fn func_call(
         Operation::Internal(f) => Ok((f)(n_args, vars, funcs)),
         Operation::External(f) => {
             for n in 0..f.arg_syms.len() {
-                vars.borrow().insert(
+                vars.borrow_mut().insert(
                     f.arg_syms[n].clone(),
                     Rc::new(list_idx(n_args.clone(), n as u128))
                 );
@@ -160,11 +160,11 @@ pub fn func_call(
 
             let result = eval(f.ast.clone(), vars.clone(), funcs, called_func.loose_syms);
             for n in 0..f.arg_syms.len() {
-                vars.borrow().remove(&f.arg_syms[n].clone());
+                vars.borrow_mut().remove(&f.arg_syms[n].clone());
             }
 
             match result {
-                Ok(r) => Ok(r.borrow().car),
+                Ok(r) => Ok(r.borrow().clone().car),
                 Err(e) => Err(e)
             }
         }