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use std::cmp::max;
pub trait PeekableIterator: Iterator {
fn peek(&mut self) -> Option<Self::Item>;
}
pub trait ForwardBackwardIterator: Iterator {
fn prev(&mut self) -> Option<Self::Item>;
}
pub trait AssertNextIterator: Iterator {
fn assert_next(&mut self, item: Self::Item) -> Result<(), ()>;
}
#[derive(Debug)]
pub struct TokenIter<'a, Item>
where
Item: 'a + PartialEq,
{
index: Option<usize>,
vector: &'a [Item],
}
impl<'a, Item> TokenIter<'a, Item>
where
Item: PartialEq,
{
pub fn new(vector: &'a [Item]) -> TokenIter<'a, Item> {
TokenIter {
index: None,
vector,
}
}
}
impl<'a, Item> PeekableIterator for TokenIter<'a, Item>
where
Item: PartialEq,
{
fn peek(&mut self) -> Option<&'a Item> {
let index = match self.index {
Some(i) => i + 1,
None => 0,
};
self.vector.get(index)
}
}
impl<'a, Item> Iterator for TokenIter<'a, Item>
where
Item: PartialEq,
{
type Item = &'a Item;
fn next(&mut self) -> Option<&'a Item> {
let index = match self.index {
Some(i) => i + 1,
None => 0,
};
self.index = Some(index);
self.vector.get(index)
}
}
impl<'a, Item> ForwardBackwardIterator for TokenIter<'a, Item>
where
Item: PartialEq,
{
fn prev(&mut self) -> Option<&'a Item> {
let index = match self.index {
None => return None,
Some(0) => {
self.index = None;
return None;
}
Some(i) => max(i - 1, 0),
};
self.index = Some(index);
self.vector.get(index)
}
}
impl<'a, Item> AssertNextIterator for TokenIter<'a, Item>
where
Item: PartialEq,
{
fn assert_next(&mut self, item: &Item) -> Result<(), ()> {
match self.next() {
Some(act) => {
if act == item {
Ok(())
} else {
Err(())
}
}
None => Err(()),
}
}
}