Introduce type aliases in syntax tree
diff --git a/syntax/ident.rs b/syntax/ident.rs
index cec424c..41eef3b 100644
--- a/syntax/ident.rs
+++ b/syntax/ident.rs
@@ -42,6 +42,7 @@
                     check(cx, &arg.ident);
                 }
             }
+            Api::TypeAlias(_alias) => unimplemented!(),
         }
     }
 }