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use crate::Node;
use std::marker::PhantomData;
/// This is how we can generically define composition of two nodes.
/// This is done generically as shown: <https://files.keavon.com/-/SurprisedGaseousAnhinga/capture.png>
/// A concrete example: <https://files.keavon.com/-/ExcitableGoldRay/capture.png>
/// And showing the direction of data flow: <https://files.keavon.com/-/SoreShimmeringElephantseal/capture.png>
/// ```text
/// ┌────────────────┐
/// T │ │ U
/// ───────────►│ Compose Node ├───────────►
/// │ │
/// └────┬───────────┤
/// ┌──────────┐ │ │
/// │ │ T -> V │ │
/// │ First ├─────────────►│ │
/// │ │ │ │
/// └──────────┘ │ │
/// ┌──────────┐ │ │
/// │ │ V -> U │ │
/// │ Second ├─────────────►│ │
/// │ │ └───────────┘
/// └──────────┘
/// ```
#[derive(Clone, Copy)]
pub struct ComposeNode<First, Second, I> {
first: First,
second: Second,
phantom: PhantomData<I>,
}
impl<'i, Input: 'i, First, Second> Node<'i, Input> for ComposeNode<First, Second, Input>
where
First: Node<'i, Input>,
Second: Node<'i, <First as Node<'i, Input>>::Output> + 'i,
{
type Output = <Second as Node<'i, <First as Node<'i, Input>>::Output>>::Output;
fn eval(&'i self, input: Input) -> Self::Output {
let arg = self.first.eval(input);
let second = &self.second;
second.eval(arg)
}
}
impl<First, Second, Input> ComposeNode<First, Second, Input> {
pub const fn new(first: First, second: Second) -> Self {
ComposeNode::<First, Second, Input> { first, second, phantom: PhantomData }
}
}
#[derive(Clone)]
pub struct AsyncComposeNode<First, Second, I> {
first: First,
second: Second,
phantom: PhantomData<I>,
}
impl<'i, Input: 'static, First, Second> Node<'i, Input> for AsyncComposeNode<First, Second, Input>
where
First: Node<'i, Input>,
First::Output: Future,
Second: Node<'i, <<First as Node<'i, Input>>::Output as Future>::Output> + 'i,
{
type Output = std::pin::Pin<Box<dyn Future<Output = <Second as Node<'i, <<First as Node<'i, Input>>::Output as Future>::Output>>::Output> + 'i>>;
fn eval(&'i self, input: Input) -> Self::Output {
Box::pin(async move {
let arg = self.first.eval(input).await;
self.second.eval(arg)
})
}
}
impl<'i, First, Second, Input: 'i> AsyncComposeNode<First, Second, Input>
where
First: Node<'i, Input>,
First::Output: Future,
Second: Node<'i, <<First as Node<'i, Input>>::Output as Future>::Output> + 'i,
{
pub const fn new(first: First, second: Second) -> Self {
AsyncComposeNode::<First, Second, Input> { first, second, phantom: PhantomData }
}
}
pub trait Then<'i, Input: 'i>: Sized {
fn then<Second>(self, second: Second) -> ComposeNode<Self, Second, Input>
where
Self: Node<'i, Input>,
Second: Node<'i, <Self as Node<'i, Input>>::Output>,
{
ComposeNode::new(self, second)
}
}
impl<'i, First: Node<'i, Input>, Input: 'i> Then<'i, Input> for First {}
pub trait AndThen<'i, Input: 'i>: Sized {
fn and_then<Second>(self, second: Second) -> AsyncComposeNode<Self, Second, Input>
where
Self: Node<'i, Input>,
Self::Output: Future,
Second: Node<'i, <<Self as Node<'i, Input>>::Output as Future>::Output> + 'i,
{
AsyncComposeNode::new(self, second)
}
}
impl<'i, First: Node<'i, Input>, Input: 'i> AndThen<'i, Input> for First {}
pub struct ConsNode<I: From<()>, Root>(pub Root, PhantomData<I>);
impl<'i, Root, Input: 'i, I: 'i + From<()>> Node<'i, Input> for ConsNode<I, Root>
where
Root: Node<'i, I>,
{
type Output = (Input, Root::Output);
fn eval(&'i self, input: Input) -> Self::Output {
let arg = self.0.eval(I::from(()));
(input, arg)
}
}
impl<'i, Root: Node<'i, I>, I: 'i + From<()>> ConsNode<I, Root> {
pub fn new(root: Root) -> Self {
ConsNode(root, PhantomData)
}
}
#[cfg(test)]
mod test {
use super::*;
use crate::generic::FnNode;
use crate::value::ValueNode;
#[test]
fn compose() {
let value = ValueNode::new(4u32);
let compose = value.then(FnNode::new(|x| x));
assert_eq!(compose.eval(()), &4u32);
let type_erased = &compose as &dyn Node<'_, (), Output = &'_ u32>;
assert_eq!(type_erased.eval(()), &4u32);
}
#[test]
fn test_ref_eval() {
let value = ValueNode::new(5);
assert_eq!(value.eval(()), &5);
let id = FnNode::new(|x| x);
let compose = ComposeNode::new(&value, &id);
assert_eq!(compose.eval(()), &5);
}
}
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