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use super::*;
use std::rc::Rc;
struct OnceCell<T>(std::cell::RefCell<Option<T>>);
impl<T> OnceCell<T> {
pub fn new() -> Self { Self(std::cell::RefCell::new(None)) }
pub fn set(&self, x: T) -> Result<(), ()> {
*self.0.try_borrow_mut().map_err(|_| ())? = Some(x);
Ok(())
}
pub fn get(&self) -> Option<std::cell::Ref<T>> { Some(std::cell::Ref::map(self.0.borrow(), |x| x.as_ref().unwrap())) }
}
pub struct Recursive<'a, I, O, E: Error<I>>(Rc<OnceCell<Box<dyn Parser<I, O, Error = E> + 'a>>>);
impl<'a, I: Clone, O, E: Error<I>> Clone for Recursive<'a, I, O, E> {
fn clone(&self) -> Self { Self(self.0.clone()) }
}
impl<'a, I: Clone, O, E: Error<I>> Parser<I, O> for Recursive<'a, I, O, E> {
type Error = E;
fn parse_inner<D: Debugger>(&self, debugger: &mut D, stream: &mut StreamOf<I, Self::Error>) -> PResult<I, O, Self::Error> {
#[allow(deprecated)]
debugger.invoke(self.0.get().expect("Recursive parser used prior to construction").as_ref(), stream)
}
fn parse_inner_verbose(&self, d: &mut Verbose, s: &mut StreamOf<I, E>) -> PResult<I, O, E> { #[allow(deprecated)] self.parse_inner(d, s) }
fn parse_inner_silent(&self, d: &mut Silent, s: &mut StreamOf<I, E>) -> PResult<I, O, E> { #[allow(deprecated)] self.parse_inner(d, s) }
}
pub fn recursive<'a, I: Clone, O, P: Parser<I, O, Error = E> + 'a, F: FnOnce(Recursive<'a, I, O, E>) -> P, E: Error<I>>(f: F) -> Recursive<'a, I, O, E> {
let rc = Rc::new(OnceCell::new());
let parser = f(Recursive(rc.clone()));
rc.set(Box::new(parser))
.unwrap_or_else(|_| unreachable!());
Recursive(rc)
}