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use std::marker::PhantomData;
use {SyntaxNodeRef, AstNode};
pub fn visitor<'a, T>() -> impl Visitor<'a, Output=T> {
EmptyVisitor { ph: PhantomData }
}
pub trait Visitor<'a>: Sized {
type Output;
fn accept(self, node: SyntaxNodeRef<'a>) -> Option<Self::Output>;
fn visit<N, F>(self, f: F) -> Vis<Self, N, F>
where N: AstNode<'a>,
F: FnOnce(N) -> Self::Output,
{
Vis { inner: self, f, ph: PhantomData }
}
}
#[derive(Debug)]
struct EmptyVisitor<T> {
ph: PhantomData<fn() -> T>
}
impl<'a, T> Visitor<'a> for EmptyVisitor<T> {
type Output = T;
fn accept(self, _node: SyntaxNodeRef<'a>) -> Option<T> {
None
}
}
#[derive(Debug)]
pub struct Vis<V, N, F> {
inner: V,
f: F,
ph: PhantomData<fn(N)>,
}
impl<'a, V, N, F> Visitor<'a> for Vis<V, N, F>
where
V: Visitor<'a>,
N: AstNode<'a>,
F: FnOnce(N) -> <V as Visitor<'a>>::Output,
{
type Output = <V as Visitor<'a>>::Output;
fn accept(self, node: SyntaxNodeRef<'a>) -> Option<Self::Output> {
let Vis { inner, f, .. } = self;
inner.accept(node).or_else(|| N::cast(node).map(f))
}
}
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