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use cargo_snippet::snippet;
#[snippet("monoid")]
pub trait Monoid: Sized {
fn identity() -> Self;
fn op(x: &Self, y: &Self) -> Self;
fn fold(v: &[Self]) -> Self {
v.iter().fold(Self::identity(), |a, b| Self::op(&a, b))
}
}
#[snippet("monoid")]
#[macro_export]
macro_rules! monoid_def {
{
$M:ident<$t:ty>,
$id:expr,
$me:expr
} => {
#[derive(Debug, Clone, Copy)]
pub struct $M($t);
impl Monoid for $M {
fn identity() -> Self {
$M($id)
}
fn op(x: &Self, y: &Self) -> Self {
let f = $me;
$M(f(x.0, y.0))
}
}
impl Into<$M> for $t {
fn into(self) -> $M {
$M(self)
}
}
};
}