41 lines
1.2 KiB
Rust
41 lines
1.2 KiB
Rust
/** Serene --- Yet an other Lisp
|
|
*
|
|
* Copyright (c) 2020 Sameer Rahmani <lxsameer@gnu.org>
|
|
*
|
|
* This program is free software; you can redistribute it and/or modify
|
|
* it under the terms of the GNU General Public License as published by
|
|
* the Free Software Foundation, either version 2 of the License.
|
|
*
|
|
* This program is distributed in the hope that it will be useful,
|
|
* but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
* GNU General Public License for more details.
|
|
*
|
|
* You should have received a copy of the GNU General Public License
|
|
* along with this program. If not, see <http://www.gnu.org/licenses/>.
|
|
*/
|
|
|
|
pub trait Seq<T> {
|
|
fn first(&self) -> &T;
|
|
fn rest(&self) -> Option<&Self>;
|
|
}
|
|
|
|
pub fn first<'a, T, S: Seq<T>>(coll: impl Into<Option<&'a S>>) -> Option<&'a T>
|
|
where
|
|
S: 'a,
|
|
{
|
|
coll.into().and_then(first)
|
|
// match coll.into() {
|
|
// Some(v) => Some(v.first()),
|
|
// None => None,
|
|
// }
|
|
}
|
|
|
|
pub fn rest<'a, T, S: Seq<T>>(coll: impl Into<Option<&'a S>>) -> Option<&'a S> {
|
|
coll.into().and_then(rest)
|
|
// match coll.into() {
|
|
// Some(v) => v.rest(),
|
|
// None => None,
|
|
// }
|
|
}
|