higher 0.2.0

/// `Pure` lets you construct a value of type `F<A>` from a single value of
/// `A`.
///
/// For instance:
///
/// * `Option::pure(5)` returns `Some(5)`.
/// * `Result::pure(5)` returns `Ok(5)`.
/// * `Vec::pure(5)` returns `vec![5]`.
pub trait Pure<A> {
    fn pure(value: A) -> Self;
}

impl<A> Pure<A> for Option<A> {
    fn pure(value: A) -> Self {
        Some(value)
    }
}

impl<A, E> Pure<A> for Result<A, E> {
    fn pure(value: A) -> Self {
        Ok(value)
    }
}

#[cfg(feature = "std")]
impl<A> Pure<A> for Vec<A> {
    fn pure(value: A) -> Self {
        vec![value]
    }
}

#[cfg(test)]
mod test {
    use crate::{Functor, Pure};

    #[test]
    fn pure_vec() {
        let a = Vec::pure(31337);
        assert_eq!(a, vec![31337]);
        let b = a.fmap(|x| x.to_string());
        assert_eq!(b, vec!["31337".to_string()]);
    }
}