[GitHub] [arrow-datafusion] Dandandan commented on a diff in pull request #3884: Improve formatting of binary expressions

[GitBox <gi...@apache.org>]

Dandandan commented on code in PR #3884:
URL: https://github.com/apache/arrow-datafusion/pull/3884#discussion_r998658717


##########
datafusion/expr/src/expr.rs:
##########
@@ -267,6 +267,28 @@ impl BinaryExpr {
     }
 }
 
+impl Display for BinaryExpr {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        // Put parentheses around child binary expressions so that we can see the difference
+        // between `(a OR b) AND c` and `a OR (b AND c)`. A future improvement here would be
+        // to only insert parentheses when needed, based on operator precedence. For example,
+        // `(a AND b) OR c` and `a AND b OR c` are equivalent and the parentheses are not
+        // necessary
+        if matches!(*self.left, Expr::BinaryExpr(_)) {
+            write!(f, "({})", self.left)?;
+        } else {
+            write!(f, "{}", self.left)?;
+        }
+        write!(f, " {} ", self.op)?;
+        if matches!(*self.right, Expr::BinaryExpr(_)) {
+            write!(f, "({})", self.right)?;
+        } else {
+            write!(f, "{}", self.right)?;
+        }
+        Ok(())
+    }
+}

Review Comment:
   I think to avoid too much parentheses we have to take into account the operator precedence.
   
   E.g. not put parentheses in these expressions:
   
   `a AND b OR c AND d`
   `a * 10 + a * 3`
   
   etc.



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