refactor: improve predicate conversion code (#325)

src/server/rpc/expr.rs

@@ -67,23 +67,21 @@ pub fn convert_predicate(predicate: Option<RPCPredicate>) -> Result<Option<Stora
     match predicate {
         // no input predicate, is fine
         None => Ok(None),
-        Some(predicate) => {
-            let RPCPredicate { root } = predicate;
-            let expr = convert_node(root)?;
-            Ok(Some(StoragePredicate { expr }))
-        }
+        Some(predicate) => match predicate.root {
+            None => EmptyPredicateNode {}.fail(),
+            Some(node) => Ok(Some(StoragePredicate {
+                expr: convert_node(node)?,
+            })),
+        },
     }
 }
 
 // converts a Node from the RPC layer into a datafusion logical expr
-fn convert_node(node: Option<RPCNode>) -> Result<Expr> {
-    match node {
-        None => EmptyPredicateNode {}.fail(),
-        Some(node) => {
+fn convert_node(node: RPCNode) -> Result<Expr> {
     let RPCNode { children, value } = node;
     let inputs = children
         .into_iter()
-                .map(|child| convert_node(Some(child)))
+        .map(convert_node)
         .collect::<Result<Vec<_>>>()?;
 
     match value {
@@ -94,8 +92,6 @@ fn convert_node(node: Option<RPCNode>) -> Result<Expr> {
         Some(value) => build_node(value, inputs),
     }
 }
-    }
-}
 
 // Builds an Expr given the Value and the converted children
 fn build_node(value: RPCValue, inputs: Vec<Expr>) -> Result<Expr> {