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%%% Copyright 2010-2011 Manolis Papadakis <manopapad@gmail.com>,
%%% Eirini Arvaniti <eirinibob@gmail.com>
%%% and Kostis Sagonas <kostis@cs.ntua.gr>
%%%
%%% This file is part of PropEr.
%%%
%%% PropEr 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 3 of the License, or
%%% (at your option) any later version.
%%%
%%% PropEr 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 PropEr. If not, see <http://www.gnu.org/licenses/>.
%%% @copyright 2010-2011 Manolis Papadakis, Eirini Arvaniti and Kostis Sagonas
%%% @version {@version}
%%% @author Manolis Papadakis
%%% @doc Auto-ADT usage example: list-based implementation of a stack, with
%%% element counting
-module(stack).
-export([is_empty/1, size/1, new/0, push/2, pop/1, safe_pop/1]).
-export_type([stack/1]).
-opaque stack(T) :: {non_neg_integer(),[T]}.
%% NOTE: You don't need to include the proper header if no properties are
%% declared in the module.
-include_lib("proper/include/proper.hrl").
%% NOTE: Every instance of the ADT in a spec must have variables as parameters.
%% When this would mean singleton variables, use variables starting with
%% an underscore.
-spec is_empty(stack(_T)) -> boolean().
is_empty({0, []}) ->
true;
is_empty({_N, [_Top|_Rest]}) ->
false.
-spec size(stack(_T)) -> non_neg_integer().
size({N, _Elems}) ->
N.
-spec new() -> stack(_T).
new() ->
{0, []}.
-spec push(T, stack(T)) -> stack(T).
push(X, {N,Elems}) ->
{N+1, [X|Elems]}.
-spec pop(stack(T)) -> {T,stack(T)}.
pop({0, []}) ->
throw(stack_empty);
pop({N, [Top|Rest]}) when N > 0 ->
{Top, {N-1,Rest}}.
-spec safe_pop(stack(T)) -> {'ok',T,stack(T)} | 'error'.
safe_pop({0, []}) ->
error;
safe_pop({N, [Top|Rest]}) when N > 0 ->
{ok, Top, {N-1,Rest}}.
%%------------------------------------------------------------------------------
%% Properties
%%------------------------------------------------------------------------------
prop_push_pop() ->
?FORALL({X,S}, {integer(),stack(integer())},
begin
{Y,_} = pop(push(X,S)),
X =:= Y
end).