yanais/examples/qgy4hbz/00.yns

(*
 * SPDX-FileCopyrightText: 2023 Alain Zscheile <fogti+devel@ytrizja.de>
 *
 * SPDX-License-Identifier: CC0-1.0
 *)
(* every object is basically a trait, just an interface *)
(* partial decomposition is possible *)

(* lets build a simple stack *)

λ $blti → {

pub let maybe = λ $T → data { :null; } λ $ →
  .{ .none = blti.unitTy; .some = blti.boxTy T; };

let stack_ds = λ $T → μ $sdst → maybe (^{ T; sdst });

pub let stack = λ $T → {
  let sdst = stack_ds T;
  pub let nil = sdst.none blti.unit;
  pub let push = λ $xs → λ $x →
    sdst.some (blti.box .{ x; xs });
};

}