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#[macro_export]
macro_rules! monad(
($M:ident, $Sig:ident, $sig_map:ident, [ $($ctx:ident,)* ]) =>
{
#[allow(dead_code)]
struct Opaque(*const u8);
// Leaf ~ Pure : a -> _M f a
// Nest ~ Roll : f (_M f a) -> _M f a
// Subs ~ Bind : (() -> _M f b) -> (b -> _M f a) -> _M f a
enum _M<'a, $($ctx,)* X> {
Leaf(X),
Nest($Sig<'a, $($ctx,)* Box<_M<'a, $($ctx,)* X>>>),
Subs( // Coyoneda f a ~ forall i. (f i, i -> a)
Box<FnOnce<(), _M<'a, $($ctx,)* Opaque>> + 'a>,
Box<FnOnce<(Opaque,), _M<'a, $($ctx,)* X>> + 'a>,
),
}
impl<'a $(,$ctx:'a)*> _M<'a, $($ctx,)* Opaque> {
// NOTE: keep this in sync with bind
#[allow(dead_code)]
#[inline]
fn _bind<Y:'a>(
self,
f: Box<FnOnce<(Opaque,), _M<'a, $($ctx,)* Y>> + 'a>,
) -> _M<'a, $($ctx,)* Y> {
match self {
_M::Subs(m, g) => {
_M::Subs(m, box move |:x|
_M::Subs(box move |:|
g.call_once((x,)), f))
},
_ => {
_M::Subs(box move |:|
self, f)
},
}
}
}
impl<'a $(,$ctx:'a)*, X:'a> _M<'a, $($ctx,)* X> {
// NOTE: keep this in sync with _bind
#[allow(dead_code)]
#[inline]
fn bind<Y:'a, F:'a>(self, f: F) -> _M<'a, $($ctx,)* Y>
where
F: FnOnce(X) -> _M<'a, $($ctx,)* Y>,
{
// calls std::mem::transmute
#[allow(dead_code)]
#[inline]
unsafe
fn lhs<'a $(,$ctx:'a)*, X:'a>(
m: _M<'a, $($ctx,)* X>,
) -> _M<'a, $($ctx,)* Opaque> {
match m {
_M::Leaf(a) => {
_M::Leaf(::std::mem::transmute(box a))
},
_M::Nest(t) => {
_M::Nest($sig_map(t, |:m2: Box<_>|
box lhs(*m2)))
},
_M::Subs(m, f) => {
_M::Subs(m, box move |:x|
lhs(f.call_once((x,))))
},
}
}
// calls std::mem::transmute
#[allow(dead_code)]
#[inline]
unsafe
fn rhs<'a $(,$ctx:'a)*, X:'a, Y:'a, F:'a>(
f: F,
) -> Box<FnOnce<(Opaque,), _M<'a, $($ctx,)* Y>> + 'a>
where
F: FnOnce(X) -> _M<'a, $($ctx,)* Y>,
{
box move |:ox|
f.call_once((*::std::mem::transmute::<_, Box<_>>(ox),))
}
// safe because we only coerce (m, f) with compatible types
match self {
_M::Subs(m, g) => {
_M::Subs(m, box move |:x| unsafe {
_M::Subs(box move |:|
lhs(g.call_once((x,))), rhs(f))
})
},
_ => { unsafe {
_M::Subs(box move |:|
lhs(self), rhs(f))
}},
}
}
#[allow(dead_code)]
#[inline]
fn resume(
mut self,
) -> Result<X, $Sig<'a, $($ctx,)* Box<_M<'a, $($ctx,)* X>>>> {
loop { match self {
_M::Leaf(a) => {
return Ok(a)
},
_M::Nest(t) => {
return Err(t)
},
_M::Subs(ma, f) => {
match ma.call_once(()) {
_M::Leaf(a) => {
self = f.call_once((a,))
},
_M::Nest(t) => {
return Err($sig_map(t,
move |:m: Box<_M<'a, $($ctx,)* _>>|
box m._bind(f)))
},
_M::Subs(mb, g) => {
self = mb
.call_once(())
._bind(box move |:pb| g
.call_once((pb,))
._bind(f))
},
}
},
}}
}
#[allow(dead_code)]
#[inline]
fn go<F>(mut self, f: F) -> X
where
// f must be a Fn since we may call it many times
F: Fn($Sig<'a, $($ctx,)* Box<_M<'a, $($ctx,)* X>>>)
-> _M<'a, $($ctx,)* X>,
{
loop { match self.resume() {
Ok(a) => {
return a
},
Err(t) => {
self = f.call((t,))
},
}}
}
}
#[allow(dead_code)]
pub struct $M<'a $(,$ctx:'a)*, X:'a>(_M<'a, $($ctx,)* X>);
impl<'a $(,$ctx:'a)*, X:'a> $M<'a, $($ctx,)* X> {
#[allow(dead_code)]
#[inline]
pub fn map<Y:'a, F:'a>(self, f: F) -> $M<'a, $($ctx,)* Y>
where
F: FnOnce(X) -> Y,
{
let $M(m) = self;
$M(m.bind(move |:x| _M::Leaf(f(x))))
}
#[allow(dead_code)]
#[inline]
pub fn point(a: X) -> $M<'a, $($ctx,)* X> {
$M(_M::Leaf(a))
}
// NOTE: keep this in sync with _bind
#[allow(dead_code)]
#[inline]
pub fn bind<Y:'a, F:'a>(self, f: F) -> $M<'a, $($ctx,)* Y>
where
F: FnOnce(X) -> $M<'a, $($ctx,)* Y>,
{
let $M(m0) = self;
$M(m0.bind(move |:x| {
let $M(m1) = f(x);
m1
}))
}
#[allow(dead_code)]
#[inline]
pub fn seq<Y:'a>(self, m: $M<'a, $($ctx,)* Y>) -> $M<'a, $($ctx,)* Y> {
self.bind(move |:_| m)
}
#[allow(dead_code)]
#[inline]
pub fn resume(self) -> Result<X, $Sig<'a, $($ctx,)* Box<$M<'a, $($ctx,)* X>>>> {
let $M(m0) = self;
match m0.resume() {
Ok(a) => {
Ok(a)
},
Err(sbmx) => {
Err($sig_map(sbmx, |:bmx: Box<_>| box $M(*bmx)))
},
}
}
#[allow(dead_code)]
#[inline]
pub fn go<F>(self, f: F) -> X
where
// f must be a Fn since we may call it many times
F: Fn($Sig<'a, $($ctx,)* Box<$M<'a, $($ctx,)* X>>>) -> $M<'a, $($ctx,)* X>,
{
let $M(m0) = self;
m0.go(|&:sbmx| {
let $M(m1) = f($sig_map(sbmx, |:bmx: Box<_>| box $M(*bmx)));
m1
})
}
}
#[allow(dead_code)]
#[inline]
pub fn point<'a $(,$ctx:'a)*, X:'a>(a: X) -> $M<'a, $($ctx,)* X> {
$M::point(a)
}
#[allow(dead_code)]
#[inline]
pub fn bind<'a $(,$ctx:'a)*, X:'a, Y:'a, F:'a>(
m: $M<'a, $($ctx,)* X>,
f: F,
) -> $M<'a, $($ctx,)* Y>
where
F: FnOnce(X) -> $M<'a, $($ctx,)* Y>,
{
m.bind(f)
}
#[allow(dead_code)]
#[inline]
pub fn wrap<'a $(,$ctx:'a)*, X:'a>(
sbmx: $Sig<'a, $($ctx,)* Box<$M<'a, $($ctx,)* X>>>
) -> $M<'a, $($ctx,)* X> {
$M(_M::Nest($sig_map(sbmx, |:bmx| {
let box $M(m) = bmx;
box m
})))
}
};
)