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use std::marker::PhantomData;
pub trait Rev {
type Input;
type Output;
fn forward(&self, i: Self::Input) -> Self::Output;
fn reverse(&self, o: Self::Output) -> Self::Input;
}
#[derive(Clone)]
pub struct Addition<A> {
amount: A
}
impl<A> Rev for Addition<A>
where
A: std::ops::Add<Output = A> + std::ops::Sub<Output = A> + Copy
{
type Input = A;
type Output = A;
fn forward(&self, a: A) -> A {
a + self.amount
}
fn reverse(&self, b: A) -> A {
b - self.amount
}
}
pub fn plus<A>(amount: A) -> Addition<A> {
Addition { amount }
}
// more blocks
#[derive(Clone)]
pub struct Negate<A>(PhantomData<A>);
impl<A: std::ops::Neg<Output = A>> Rev for Negate<A> {
type Input = A;
type Output = A;
fn forward(&self, a: Self::Input) -> Self::Output {
-a
}
fn reverse(&self, b: Self::Output) -> Self::Input {
-b
}
}
pub fn neg<A>() -> Negate<A> {
Negate(PhantomData)
}
#[derive(Clone)]
pub struct Multiplication<A> {
amount: A
}
impl<A> Rev for Multiplication<A>
where
A: std::ops::Mul<Output = A> + std::ops::Div<Output = A> + Copy,
{
type Input = A;
type Output = A;
fn forward(&self, a: A) -> A {
a * self.amount
}
fn reverse(&self, b: A) -> A {
b / self.amount
}
}
pub fn times<A>(amount: A) -> Multiplication<A> {
Multiplication { amount }
}
#[derive(Clone)]
pub struct DiscreteMap<A, B>(Vec<(A, B)>);
impl<A: PartialEq + Clone, B: PartialEq + Clone> Rev for DiscreteMap<A, B> {
type Input = A;
type Output = B;
fn forward(&self, a: A) -> B {
for i in self.0.iter() {
if i.0 == a {
return i.1.clone()
}
}
panic!()
}
fn reverse(&self, b: B) -> A {
for i in self.0.iter() {
if i.1 == b {
return i.0.clone()
}
}
panic!()
}
}
pub fn discrete<A, B>(vec: Vec<(A, B)>) -> DiscreteMap<A, B> {
DiscreteMap(vec)
}
// combinators
#[derive(Clone)]
pub struct Pipe<X, Y>(X, Y);
impl<X, Y> Rev for Pipe<X, Y>
where
X: Rev,
Y: Rev<Input = X::Output>
{
type Input = X::Input;
type Output = Y::Output;
fn forward(&self, a: Self::Input) -> Self::Output {
self.1.forward(self.0.forward(a))
}
fn reverse(&self, c: Self::Output) -> Self::Input {
self.0.reverse(self.1.reverse(c))
}
}
#[derive(Clone)]
pub struct Inverse<X>(X);
impl<X: Rev> Rev for Inverse<X> {
type Input = X::Output;
type Output = X::Input;
fn forward(&self, a: Self::Input) -> Self::Output {
self.0.reverse(a)
}
fn reverse(&self, b: Self::Output) -> Self::Input {
self.0.forward(b)
}
}
pub trait RevExt: Rev + Sized {
fn then<N: Rev<Input = Self::Output>>(self, other: N) -> Pipe<Self, N> {
Pipe(self, other)
}
fn inverse(self) -> Inverse<Self> {
Inverse(self)
}
}
impl<T: Rev> RevExt for T {}
pub fn under<Op, Val>(op: Op, val: Val) -> impl Rev<Input = Op::Input, Output = Op::Input>
where
Op: Rev + Clone,
Val: Rev<Input = Op::Output, Output = Op::Output>
{
op.clone().then(val).then(op.inverse())
}
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