137 lines
3.5 KiB
Rust
137 lines
3.5 KiB
Rust
//! Helper [Monad]s to defer execution until necessary.
|
|
//! Wrapped value is just a box pointing to the constructor function.
|
|
//!
|
|
//! Due to semantical laziness,
|
|
//! [`LazyInstance::replace`] and [`LazyInstance::discard_first`]/[`LazyInstance::discard_second`]
|
|
//! actually fully cancel the "unnecessary" computation.
|
|
//!
|
|
//! For stackless execution see [`stackless`].
|
|
//!
|
|
//! [`stackless`]: super::stackless
|
|
|
|
use crate::func::class_prelude::*;
|
|
|
|
pub struct LazyInstance;
|
|
|
|
impl WeakFunctorAny for LazyInstance {
|
|
type FAny<'a, A: 'a + Send> = Box<dyn 'a + Send + FnOnce() -> A>;
|
|
}
|
|
|
|
impl<'a> Functor<'a> for LazyInstance {
|
|
fn fmap<A: 'a + Send, B: 'a + Send>(
|
|
fa: Self::F<A>,
|
|
f: impl 'a + Send + FnOnce(A) -> B,
|
|
) -> Self::F<B> {
|
|
Box::new(|| f(fa()))
|
|
}
|
|
|
|
fn replace<A: 'a + Send, B: 'a + Send>(fa: Self::F<A>, b: B) -> Self::F<B> {
|
|
drop(fa);
|
|
Box::new(|| b)
|
|
}
|
|
|
|
fn void<A: 'a + Send>(fa: Self::F<A>) -> Self::F<()> {
|
|
drop(fa);
|
|
Box::new(|| ())
|
|
}
|
|
}
|
|
|
|
impl<'a> Pure<'a> for LazyInstance {
|
|
fn pure<A: 'a + Send>(a: A) -> Self::F<A> {
|
|
Box::new(|| a)
|
|
}
|
|
}
|
|
|
|
impl<'a> ApplicativeSeq<'a> for LazyInstance {
|
|
fn seq<A: 'a + Send, B: 'a + Send>(
|
|
ff: Self::F<impl 'a + Send + FnOnce(A) -> B>,
|
|
fa: Self::F<A>,
|
|
) -> Self::F<B> {
|
|
Box::new(|| ff()(fa()))
|
|
}
|
|
}
|
|
|
|
impl<'a> ApplicativeLA2<'a> for LazyInstance {
|
|
fn la2<A: 'a + Send, B: 'a + Send, C: 'a + Send>(
|
|
fa: Self::F<A>,
|
|
fb: Self::F<B>,
|
|
f: impl 'a + Send + FnOnce(A, B) -> C,
|
|
) -> Self::F<C> {
|
|
Box::new(|| f(fa(), fb()))
|
|
}
|
|
}
|
|
|
|
impl<'a> ApplicativeTuple<'a> for LazyInstance {
|
|
fn tuple<A: 'a + Send, B: 'a + Send>((fa, fb): (Self::F<A>, Self::F<B>)) -> Self::F<(A, B)> {
|
|
Box::new(|| (fa(), fb()))
|
|
}
|
|
}
|
|
|
|
impl<'a> ApplicativeSelect<'a> for LazyInstance {}
|
|
|
|
impl<'a> Applicative<'a> for LazyInstance {
|
|
fn discard_first<A: 'a + Send, B: 'a + Send>(fa: Self::F<A>, fb: Self::F<B>) -> Self::F<B> {
|
|
drop(fa);
|
|
fb
|
|
}
|
|
|
|
fn discard_second<A: 'a + Send, B: 'a + Send>(fa: Self::F<A>, fb: Self::F<B>) -> Self::F<A> {
|
|
drop(fb);
|
|
fa
|
|
}
|
|
}
|
|
|
|
impl<'a> Monad<'a> for LazyInstance {
|
|
fn bind<A: 'a + Send, B: 'a + Send>(
|
|
fa: Self::F<A>,
|
|
f: impl 'a + Send + FnOnce(A) -> Self::F<B>,
|
|
) -> Self::F<B> {
|
|
Box::new(|| f(fa())())
|
|
}
|
|
|
|
fn iterate<B: 'a + Send>(mut f: impl Iterative<'a, T = Self, B = B>) -> Self::F<B> {
|
|
loop {
|
|
match f.next()() {
|
|
ControlFlow::Continue(next_f) => f = next_f,
|
|
ControlFlow::Break(b) => return Self::pure(b),
|
|
}
|
|
}
|
|
}
|
|
|
|
fn join<A: 'a + Send>(ffa: Self::F<Self::F<A>>) -> Self::F<A> {
|
|
Box::new(|| ffa()())
|
|
}
|
|
}
|
|
|
|
#[cfg(test)]
|
|
mod lazy_tests {
|
|
use std::sync::Arc;
|
|
|
|
use super::{test_suite, tests, LazyInstance};
|
|
|
|
type T = LazyInstance;
|
|
|
|
impl<'a> tests::Eqr<'a> for T {
|
|
fn eqr<A: 'a + Send + PartialEq + std::fmt::Debug>(
|
|
name: &'a str,
|
|
left: Self::F<A>,
|
|
right: Self::F<A>,
|
|
) -> tests::R {
|
|
tests::eqr(name, left(), right())
|
|
}
|
|
}
|
|
|
|
impl<'a> test_suite::FunctorTestSuite<'a> for T {
|
|
fn sample<A: 'a + Send, F: FnMut(Arc<dyn test_suite::WrapFunction<'a, A, Self::F<A>>>)>(
|
|
mut f: F,
|
|
) {
|
|
f(Arc::new(|a| Box::new(|| a)));
|
|
}
|
|
}
|
|
|
|
#[test]
|
|
fn monad_follows_laws() {
|
|
test_suite::monad_follows_laws::<T>().unwrap();
|
|
}
|
|
}
|