From 1959b1833ed2be1a19b4568f196471212824ab97 Mon Sep 17 00:00:00 2001
From: timofey <tim@ongoteam.yaconnect.com>
Date: Mon, 31 Jul 2023 16:16:14 +0000
Subject: [PATCH] `stackless::atom`

---
 src/func/instances/stackless.rs | 89 +++++++++++++++++++++------------
 1 file changed, 58 insertions(+), 31 deletions(-)

diff --git a/src/func/instances/stackless.rs b/src/func/instances/stackless.rs
index d862ef8..1ea8f57 100644
--- a/src/func/instances/stackless.rs
+++ b/src/func/instances/stackless.rs
@@ -5,13 +5,46 @@
 //!
 //! [`lazy`]: super::lazy
 
+use std::marker::PhantomData;
 use std::{cell::Cell, rc::Rc};
 
 use crate::func::class_prelude::*;
 use crate::func::derivations::{ApplicativeLA2ViaSeq, ApplicativeTupleViaLA2};
 
+trait Atom {
+    fn next<'t>(self: Box<Self>) -> Oet<'t>
+    where
+        Self: 't;
+}
+
+struct Wrapper<'a, F>(F, PhantomData<&'a ()>);
+
+fn atom<'a, F: 'a + FnOnce() -> Oet<'a>>(f: F) -> EvalTree<'a> {
+    EvalTree::Atom(Box::new(Wrapper(f, PhantomData)))
+}
+
+fn batom<'a, F: 'a + FnOnce() -> Oet<'a>>(f: F) -> Box<EvalTree<'a>> {
+    Box::new(atom(f))
+}
+
+fn satom<'a, F: 'a + FnOnce() -> Oet<'a>>(f: F) -> Oet<'a> {
+    Some(atom(f))
+}
+
+impl<'a, F> Atom for Wrapper<'a, F>
+where
+    F: 'a + FnOnce() -> Oet<'a>,
+{
+    fn next<'t>(self: Box<Self>) -> Oet<'t>
+    where
+        Self: 't,
+    {
+        (self.0)()
+    }
+}
+
 enum EvalTree<'a> {
-    Atom(Box<dyn 'a + FnOnce() -> Oet<'a>>),
+    Atom(Box<dyn 'a + Atom>),
     Composite(Box<EvalTree<'a>>, Box<EvalTree<'a>>),
 }
 
@@ -20,9 +53,9 @@ type Oet<'a> = Option<EvalTree<'a>>;
 impl<'a> EvalTree<'a> {
     fn next(self) -> Oet<'a> {
         match self {
-            Self::Atom(f) => f(),
+            Self::Atom(f) => f.next(),
             Self::Composite(etl, etr) => match *etl {
-                Self::Atom(f) => match f() {
+                Self::Atom(f) => match f.next() {
                     Some(newleft) => Some(Self::Composite(Box::new(newleft), etr)),
                     None => Some(*etr),
                 },
@@ -63,13 +96,11 @@ impl<'a, A: 'a> Stackless<'a, A> {
             let cell_l = Rc::new(Cell::new(None));
             let cell_r = cell_l.clone();
             Some(EvalTree::Composite(
-                Box::new(EvalTree::Atom(Box::new(move || {
-                    self.call(move |a| set_cell(cell_l, a))
-                }))),
-                Box::new(EvalTree::Atom(Box::new(move || {
+                batom(move || self.call(move |a| set_cell(cell_l, a))),
+                batom(move || {
                     let stackless = f(get_cell(cell_r));
-                    Some(EvalTree::Atom(Box::new(|| stackless.0(takesb))))
-                }))),
+                    satom(|| stackless.0(takesb))
+                }),
             ))
         }))
     }
@@ -80,16 +111,14 @@ impl<'a, A: 'a> Stackless<'a, A> {
             let cell_l = Rc::new(Cell::new(None));
             let cell_r = cell_l.clone();
             Some(EvalTree::Composite(
-                Box::new(EvalTree::Atom(Box::new(move || {
-                    self.call(move |a| set_cell(cell_l, a))
-                }))),
-                Box::new(EvalTree::Atom(Box::new(move || {
+                batom(move || self.call(move |a| set_cell(cell_l, a))),
+                batom(move || {
                     let b = f(get_cell(cell_r));
-                    Some(EvalTree::Atom(Box::new(|| {
+                    satom(|| {
                         takesb(b);
                         None
-                    })))
-                }))),
+                    })
+                }),
             ))
         }))
     }
@@ -110,10 +139,10 @@ impl<'a, A: 'a> Stackless<'a, A> {
 impl<'a, A: 'a> From<A> for Stackless<'a, A> {
     fn from(value: A) -> Self {
         Stackless(Box::new(|takesa| {
-            Some(EvalTree::Atom(Box::new(|| {
+            satom(|| {
                 takesa(value);
                 None
-            })))
+            })
         }))
     }
 }
@@ -132,11 +161,11 @@ impl<'a> Functor<'a> for StacklessInstance {
     fn replace<A: 'a, B: 'a>(fa: Self::F<A>, b: B) -> Self::F<B> {
         Stackless(Box::new(|takesb| {
             Some(EvalTree::Composite(
-                Box::new(EvalTree::Atom(Box::new(move || fa.call(drop)))),
-                Box::new(EvalTree::Atom(Box::new(move || {
+                batom(move || fa.call(drop)),
+                batom(move || {
                     takesb(b);
                     None
-                }))),
+                }),
             ))
         }))
     }
@@ -176,8 +205,8 @@ impl<'a> Applicative<'a> for StacklessInstance {
     fn discard_first<A: 'a, B: 'a>(fa: Self::F<A>, fb: Self::F<B>) -> Self::F<B> {
         Stackless(Box::new(|takesb| {
             Some(EvalTree::Composite(
-                Box::new(EvalTree::Atom(Box::new(|| fa.call(drop)))),
-                Box::new(EvalTree::Atom(Box::new(|| fb.0(takesb)))),
+                batom(|| fa.call(drop)),
+                batom(|| fb.0(takesb)),
             ))
         }))
     }
@@ -185,8 +214,8 @@ impl<'a> Applicative<'a> for StacklessInstance {
     fn discard_second<A: 'a, B: 'a>(fa: Self::F<A>, fb: Self::F<B>) -> Self::F<A> {
         Stackless(Box::new(|takesa| {
             Some(EvalTree::Composite(
-                Box::new(EvalTree::Atom(Box::new(|| fa.0(takesa)))),
-                Box::new(EvalTree::Atom(Box::new(|| fb.call(drop)))),
+                batom(|| fa.0(takesa)),
+                batom(|| fb.call(drop)),
             ))
         }))
     }
@@ -211,13 +240,11 @@ impl<'a> Monad<'a> for StacklessInstance {
             let cell_l = Rc::new(Cell::new(None));
             let cell_r = cell_l.clone();
             Some(EvalTree::Composite(
-                Box::new(EvalTree::Atom(Box::new(move || {
-                    ffa.call(move |a| set_cell(cell_l, a))
-                }))),
-                Box::new(EvalTree::Atom(Box::new(move || {
+                batom(move || ffa.call(move |a| set_cell(cell_l, a))),
+                batom(move || {
                     let stackless = get_cell(cell_r);
-                    Some(EvalTree::Atom(Box::new(|| stackless.0(takesa))))
-                }))),
+                    satom(|| stackless.0(takesa))
+                }),
             ))
         }))
     }