treaty -


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use effectful::{
    effective::Effective,
    environment::{DynBind, Environment, NativeForm},
    for_lt,
    higher_ranked::Mut,
};

use crate::{
    any::TypeName,
    hkt::Marker,
    protocol::{DynVisitor, DynWalker},
};

use super::VisitResult;

/// Protocol for requesting a hint from a visitor.
pub trait RequestHint<'ctx, E: Environment>: DynBind<E> {
    /// Call this to request a hint.
    ///
    /// `walker` is what the visitor (`self`) will call to give a hint using the
    /// [`Hint`][crate::builtins::walker::Hint] protocol.
    fn request_hint<'this: 'e, 'walker: 'e, 'e>(
        &'this mut self,
        walker: DynWalker<'walker, 'ctx, E>,
    ) -> NativeForm<'e, VisitResult, E>
    where
        'ctx: 'this + 'walker;
}

pub struct RequestHintProto<E: Environment>(Marker<E>);

impl<'a, 'ctx, E> TypeName::MemberTypeForLt<'a, 'ctx, E, &'a &'ctx ()> for RequestHintProto<E>
where
    E: Environment,
{
    type T = dyn RequestHint<'ctx, E> + 'a;
}

impl<'a, 'ctx, E> TypeName::LowerTypeWithBound<'a, 'ctx, E, &'a &'ctx ()>
    for dyn RequestHint<'ctx, E> + 'a
where
    E: Environment,
{
    type Higher = RequestHintProto<E>;
}

/// Visit using the [`RequestHint`] protocol.
///
/// If [`Flow::Continue`] is returned then the visitor wants/needs more information it didn't get
/// from the hints.
/// If [`Flow::Done`] is returned then the visitor doesn't need any more information and the walker
/// should stop walking.
/// If [`Flow::Break`] is returned then there was an error and the walker should stop walking.
pub fn request_hint<'ctx: 'visitor + 'walker, 'visitor: 'e, 'walker: 'e, 'e, E: Environment>(
    visitor: DynVisitor<'visitor, 'ctx, E>,
    walker: DynWalker<'walker, 'ctx, E>,
) -> NativeForm<'e, VisitResult<DynWalker<'walker, 'ctx, E>>, E> {
    E::value(walker)
        .update(visitor, |visitor, walker| {
            if let Some(object) = visitor.0.upcast_mut::<RequestHintProto<E>>() {
                // Allow the visitor to give a hint if it wants.
                object
                    .request_hint(walker.cast())
                    .map((), |_, x| x.unit_skipped())
                    .cast::<()>();

                todo!()
            } else {
                // If the visitor doesn't support request hint then we continue.
                E::value(VisitResult::Skipped(())).cast()
            }
        })
        .map((), |_, (walker, result)| result.map_skipped(|_| walker))
        .cast()
}