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use crate::TransformArgs;
use expr::MirRelationExpr;
#[derive(Debug)]
pub struct Project;
impl crate::Transform for Project {
fn transform(
&self,
relation: &mut MirRelationExpr,
_: TransformArgs,
) -> Result<(), crate::TransformError> {
relation.try_visit_mut_pre(&mut |e| Ok(self.action(e)))
}
}
impl Project {
pub fn action(&self, relation: &mut MirRelationExpr) {
if let MirRelationExpr::Project { input, outputs } = relation {
while let MirRelationExpr::Project {
input: inner,
outputs: outputs2,
} = &mut **input
{
*outputs = outputs.iter().map(|i| outputs2[*i]).collect();
**input = inner.take_dangerous();
}
if outputs.iter().enumerate().all(|(a, b)| a == *b) && outputs.len() == input.arity() {
*relation = input.take_dangerous();
}
}
}
}