Using PrattParser with arenas?

[viridia]

I'm attempting to use the PrattParser, but I also want my AST nodes to be allocated in an arena. The problem is that the arena reference needs to be captured in the closures that I pass to the PrattParser; this works fine for simple expressions, but not for recursive ones.

fn to_ast<'a>(arena: &'a mut Arena<Node<'a>>, expression: Pairs<Rule>) -> &'a ast::Node<'a> {
    PRATT_PARSER
        .map_primary(|primary| {
            let location: TokenLocation = primary.as_span().into();
            match primary.as_rule() {
                // ERROR: Captured variable cannot escape `FnMut` closure body
                Rule::expr => to_ast(arena, primary.into_inner()),
                Rule::integer => {
                    let value = primary.as_str().parse::<i64>().unwrap();
                    arena.new_node(ast::Node {
                        location,
                        value: ast::NodeValue::ConstI64(value),
                    })
                }
                _ => todo!("to_ast: {:?}", primary),
            }
        })
        // etc...details omitted

Any ideas how to get around this limitation?

Right now the only option I can think of is to not use PrattParser, and write my own operator-precedence algorithm that doesn't use closures.

[viridia]

Never mind, I figured it out :) Arenas don't need to be mutable references, something I did not expect.