//@NO-IMPLICIT-PRELUDE
//! Implementation of the `Monoid` type

let { Semigroup } = import! std.semigroup

/// `Monoid a` represents an semigroup an which has an identity. This means
/// the following additional laws must hold:
///
/// * `forall x . append x empty == x`
/// * `forall x . append empty x == x`
#[implicit]
type Monoid a = {
    semigroup : Semigroup a,
    /// # Note
    ///
    /// * Known as `mempty` in Haskell
    empty : a
}

let empty ?m : [Monoid a] -> a = m.empty

{
    Monoid,
    empty,
}