Function implement

src/transform/src/normalize_lets.rs:1009–1043

(
        relation: &mut MirRelationExpr,
        remap: &BTreeMap<LocalId, LocalId>,
    )

    }

    fn implement(
        relation: &mut MirRelationExpr,
        remap: &BTreeMap<LocalId, LocalId>,
    ) -> Result<(), crate::TransformError> {
        let mut worklist = vec![relation];
        while let Some(expr) = worklist.pop() {
            match expr {
                MirRelationExpr::Let { id, .. } => {
                    *id = *remap
                        .get(id)
                        .ok_or(crate::TransformError::IdentifierMissing(*id))?;
                }
                MirRelationExpr::LetRec { ids, .. } => {
                    for id in ids.iter_mut() {
                        *id = *remap
                            .get(id)
                            .ok_or(crate::TransformError::IdentifierMissing(*id))?;
                    }
                }
                MirRelationExpr::Get {
                    id: Id::Local(id), ..
                } => {
                    *id = *remap
                        .get(id)
                        .ok_or(crate::TransformError::IdentifierMissing(*id))?;
                }
                _ => {
                    // Remapped identifiers not used in these patterns.
                }
            }
            // The order is not critical, but behave as a stack for clarity.
            worklist.extend(expr.children_mut().rev());
        }
        Ok(())
    }
}