fix unify query

src/data/keyword.rs

@@ -40,6 +40,9 @@ impl Keyword {
                 .0
                 .starts_with(['_', ':', '<', '.', '*', '#', '$', '?', '!', ']', '['])
     }
+    pub(crate) fn is_query_var(&self) -> bool {
+        self.0.starts_with('?') && self.0.len() > 1
+    }
     pub(crate) fn validate_not_reserved(&self) -> Result<()> {
         ensure!(
             !self.is_reserved(),

src/data/value.rs

@@ -100,7 +100,8 @@ impl DataValue {
     pub(crate) fn get_entity_id(&self) -> Result<EntityId> {
         match self {
             DataValue::EnId(id) => Ok(*id),
-            v => bail!("type mismatch: expect type {:?}, got value {:?}", self, v),
+            DataValue::Int(id) => Ok(EntityId(*id as u64)),
+            v => bail!("type mismatch: expect type EntId, got value {:?}", self),
         }
     }
 }

src/parse/query.rs

@@ -186,7 +186,7 @@ impl SessionTx {
             .ok_or_else(|| anyhow!("expect field 'unify' to be a keyword"))?;
         let binding = Keyword::from(binding);
         ensure!(
-            !binding.is_reserved(),
+            binding.is_query_var(),
             "binding for unification {} is reserved",
             binding
         );