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use core::marker::PhantomData;
use canonical::{Canon, CanonError};
use crate::branch::Branch;
use crate::branch_mut::BranchMut;
use crate::compound::{Child, Compound, MutableLeaves};
pub enum Step {
Found(usize),
Into(usize),
Advance,
Abort,
}
pub struct Walk<'a, C, A> {
ofs: usize,
compound: &'a C,
_marker: PhantomData<A>,
}
impl<'a, C, A> Walk<'a, C, A>
where
C: Compound<A>,
{
pub(crate) fn new(compound: &'a C, ofs: usize) -> Self {
Walk {
ofs,
compound,
_marker: PhantomData,
}
}
pub fn child(&self, ofs: usize) -> Child<'a, C, A> {
self.compound.child(ofs + self.ofs)
}
}
pub trait Walker<C, A>
where
C: Compound<A>,
{
fn walk(&mut self, walk: Walk<C, A>) -> Step;
}
pub struct AllLeaves;
impl<C, A> Walker<C, A> for AllLeaves
where
C: Compound<A>,
{
fn walk(&mut self, walk: Walk<C, A>) -> Step {
for i in 0.. {
match walk.child(i) {
Child::Leaf(_) => return Step::Found(i),
Child::Node(_) => return Step::Into(i),
Child::Empty => (),
Child::EndOfNode => return Step::Advance,
}
}
unreachable!()
}
}
pub trait First<'a, A>
where
Self: Compound<A>,
{
fn first(&'a self) -> Result<Option<Branch<'a, Self, A>>, CanonError>;
fn first_mut(
&'a mut self,
) -> Result<Option<BranchMut<'a, Self, A>>, CanonError>
where
Self: MutableLeaves + Clone;
}
impl<'a, C, A> First<'a, A> for C
where
C: Compound<A>,
A: Canon,
{
fn first(&'a self) -> Result<Option<Branch<'a, Self, A>>, CanonError> {
Branch::<_, A>::walk(self, AllLeaves)
}
fn first_mut(
&'a mut self,
) -> Result<Option<BranchMut<'a, Self, A>>, CanonError>
where
C: MutableLeaves + Clone,
{
BranchMut::<_, A>::walk(self, AllLeaves)
}
}