Macro rsmonad::functor

macro_rules! functor {
    ($name:ident<A $(, $($g_ty:ident $(: $g_bound:path $(, $g_bounds:path)*)?),+)?>: fn fmap($self:ident, $f:ident) $fmap:block) => { ... };
}

Implement Functor (and its superclasses automatically) after a definition.

use rsmonad::prelude::*;

#[derive(Debug, PartialEq)]
struct Pointless<A>(A);

functor! {
    Pointless<A>:

    fn fmap(self, f) {
        Pointless(f(self.0))
    }
}

assert_eq!(Pointless(4) % u8::is_power_of_two, Pointless(true));