Method fold_expr

prqlc/prqlc/src/sql/pq/preprocess.rs:603–630

(&mut self, expr: Expr)

impl RqFold for Normalizer {
    fn fold_expr(&mut self, expr: Expr) -> Result<Expr> {
        let expr = Expr {
            kind: rq::fold_expr_kind(self, expr.kind)?,
            ..expr
        };

        if let ExprKind::Operator { name, args } = &expr.kind {
            if name == "std.eq" && args.len() == 2 {
                let (left, right) = (&args[0], &args[1]);
                let span = expr.span;
                let new_args = if let ExprKind::Literal(Literal::Null) = &left.kind {
                    vec![right.clone(), left.clone()]
                } else {
                    vec![left.clone(), right.clone()]
                };
                let new_kind = ExprKind::Operator {
                    name: name.clone(),
                    args: new_args,
                };
                return Ok(Expr {
                    kind: new_kind,
                    span,
                });
            }
        }

        Ok(expr)
    }
}