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// Copyright (C) 2026 Industrial Algebra
// SPDX-License-Identifier: Apache-2.0
/// Monadic do-notation sugar.
///
/// Desugars sequential `x = expr` bindings into nested `Chain::chain` calls.
///
/// # Example
/// ```ignore
/// do_! { OptionF;
/// x = Some(1);
/// y = Some(x + 1);
/// OptionF::pure(x + y)
/// }
/// ```
#[macro_export]
macro_rules! do_ {
// Terminal: just an expression (no more bindings)
($F:ty; $e:expr) => {
$e
};
// Binding: x = expr; rest...
($F:ty; $x:ident = $e:expr; $($rest:tt)+) => {
<$F as $crate::chain::Chain>::chain($e, |$x| {
$crate::do_!($F; $($rest)+)
})
};
}
/// Applicative do-notation sugar.
///
/// Collects independent bindings and combines them with `ap`/`fmap`.
/// Supports 1–4 bindings followed by `yield expr`.
///
/// # Example
/// ```ignore
/// ado_! { OptionF;
/// x = Some(1);
/// y = Some(2);
/// yield x + y
/// }
/// ```
#[macro_export]
macro_rules! ado_ {
// 1 binding
($F:ty; $x:ident = $e:expr; yield $body:expr) => {
<$F as $crate::functor::Functor>::fmap($e, |$x| $body)
};
// 2 bindings
($F:ty; $x1:ident = $e1:expr; $x2:ident = $e2:expr; yield $body:expr) => {
<$F as $crate::apply::Apply>::ap(
<$F as $crate::functor::Functor>::fmap($e1, |$x1| move |$x2| $body),
$e2,
)
};
// 3 bindings
($F:ty;
$x1:ident = $e1:expr;
$x2:ident = $e2:expr;
$x3:ident = $e3:expr;
yield $body:expr
) => {
<$F as $crate::apply::Apply>::ap(
<$F as $crate::apply::Apply>::ap(
<$F as $crate::functor::Functor>::fmap($e1, |$x1| move |$x2| move |$x3| $body),
$e2,
),
$e3,
)
};
// 4 bindings
($F:ty;
$x1:ident = $e1:expr;
$x2:ident = $e2:expr;
$x3:ident = $e3:expr;
$x4:ident = $e4:expr;
yield $body:expr
) => {
<$F as $crate::apply::Apply>::ap(
<$F as $crate::apply::Apply>::ap(
<$F as $crate::apply::Apply>::ap(
<$F as $crate::functor::Functor>::fmap($e1, |$x1| {
move |$x2| move |$x3| move |$x4| $body
}),
$e2,
),
$e3,
),
$e4,
)
};
}
#[cfg(test)]
mod tests {
use crate::applicative::Applicative;
use crate::hkt::OptionF;
#[cfg(any(feature = "std", feature = "alloc"))]
use crate::hkt::VecF;
#[test]
fn do_option_some() {
let result = do_! { OptionF;
x = Some(1);
y = Some(x + 1);
OptionF::pure(x + y)
};
assert_eq!(result, Some(3));
}
#[test]
fn do_option_none() {
let result: Option<i32> = do_! { OptionF;
x = Some(1);
_y = None::<i32>;
OptionF::pure(x)
};
assert_eq!(result, None);
}
#[test]
fn do_option_single() {
let result = do_! { OptionF;
Some(42)
};
assert_eq!(result, Some(42));
}
#[test]
fn do_vec() {
let result = do_! { VecF;
x = vec![1, 2];
y = vec![10, 20];
VecF::pure(x + y)
};
assert_eq!(result, vec![11, 21, 12, 22]);
}
#[test]
fn ado_option_1() {
let result = ado_! { OptionF;
x = Some(5);
yield x * 2
};
assert_eq!(result, Some(10));
}
#[test]
fn ado_option_2() {
let result = ado_! { OptionF;
x = Some(1);
y = Some(2);
yield x + y
};
assert_eq!(result, Some(3));
}
#[test]
fn ado_option_2_none() {
let result = ado_! { OptionF;
x = Some(1);
y = None::<i32>;
yield x + y
};
assert_eq!(result, None);
}
#[test]
fn ado_option_3() {
let result = ado_! { OptionF;
x = Some(1);
y = Some(2);
z = Some(3);
yield x + y + z
};
assert_eq!(result, Some(6));
}
#[test]
fn ado_option_4() {
let result = ado_! { OptionF;
a = Some(1);
b = Some(2);
c = Some(3);
d = Some(4);
yield a + b + c + d
};
assert_eq!(result, Some(10));
}
#[test]
fn ado_vec_2() {
let result = ado_! { VecF;
x = vec![1, 2];
y = vec![10, 20];
yield x + y
};
assert_eq!(result, vec![11, 21, 12, 22]);
}
}