treaty -


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57

use crate::{
    any::TypeName,
    effect::{Effect, ErasedEffective, ReadyExt as _},
    hkt::Marker,
    protocol::{DynVisitor, DynWalker},
};

use super::VisitResult;

/// Protocol for requesting a hint from a visitor.
pub trait RequestHint<'ctx, E: Effect> {
    /// 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<'a>(
        &'a mut self,
        walker: DynWalker<'a, 'ctx>,
    ) -> ErasedEffective<'a, VisitResult<DynWalker<'a, 'ctx>>, E>;
}

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

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

impl<'a, 'ctx, E> TypeName::LowerTypeWithBound<'a, 'ctx, &'a &'ctx ()>
    for dyn RequestHint<'ctx, E> + Send + Sync + 'a
where
    E: Effect,
{
    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<'a, 'ctx, E: Effect>(
    visitor: DynVisitor<'a, 'ctx>,
    walker: DynWalker<'a, 'ctx>,
) -> ErasedEffective<'a, VisitResult<DynWalker<'a, 'ctx>>, E> {
    if let Some(object) = visitor.0.upcast_mut::<RequestHintProto<E>>() {
        // Allow the visitor to give a hint if it wants.
        object.request_hint(walker)
    } else {
        // If the visitor doesn't support request hint then we continue.
        VisitResult::Skipped(walker).ready()
    }
}