Merge pull request #280 from erg-lang/fix-#278

Fix #278

compiler/erg_compiler/context/eval.rs

@@ -1169,6 +1169,7 @@ impl Context {
                     if !st.is_generalized() {
                         self.substitute_typarams(&qt, &st);
                     }
+                    self.sub_unify(&st, &qt, Location::Unknown, None).unwrap();
                 }
                 _ => {}
             }

compiler/erg_compiler/context/tyvar.rs

@@ -1391,7 +1391,8 @@ impl Context {
                 Ok(())
             }
             (Type::FreeVar(lfv), _) if lfv.is_unbound() => {
-                match &mut *lfv.borrow_mut() {
+                let lfv_ref = unsafe { lfv.as_ptr().as_mut().unwrap() };
+                match lfv_ref {
                     FreeKind::NamedUnbound { constraint, .. }
                     | FreeKind::Unbound { constraint, .. } => match constraint {
                         // sub !<: r => Error