yjshen removed a comment on pull request #1970:
URL:
https://github.com/apache/arrow-datafusion/pull/1970#issuecomment-1064154488
```rust
struct Print{}
impl ExpressionVisitor for Print {
fn pre_visit(self, expr: &Expr) ->
datafusion_common::Result<Recursion<Self>> where Self: ExpressionVisitor {
println!("pre {}", expr);
Ok(Recursion::Continue(self))
}
fn post_visit(self, expr: &Expr) -> datafusion_common::Result<Self> {
println!("post {}", expr);
Ok(self)
}
}
#[test]
fn a() {
let a = BinaryExpr {
left: Box::new(Expr::Column(Column::from_name("foo"))),
op: Operator::Gt,
right: Box::new(Expr::Column(Column::from_name("bar")))
};
a.accept(Print{}).unwrap();
}
```
and I get
```
pre #foo > #bar
pre #foo
post #foo
pre #bar
post #bar
post #foo > #bar
```
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