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%% The contents of this file are subject to the Mozilla Public License
%% Version 1.1 (the "License"); you may not use this file except in
%% compliance with the License. You may obtain a copy of the License
%% at http://www.mozilla.org/MPL/
%%
%% Software distributed under the License is distributed on an "AS IS"
%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
%% the License for the specific language governing rights and
%% limitations under the License.
%%
%% The Original Code is Erlando.
%%
%% The Initial Developer of the Original Code is VMware, Inc.
%% Copyright (c) 2011-2013 VMware, Inc. All rights reserved.
%%
-module(maybe_m).
-export_type([maybe/1]).
-behaviour(monad).
-export(['>>='/2, return/1, fail/1]).
-behaviour(monad_plus).
-export([mzero/0, mplus/2]).
-type maybe(A) :: {just, A} | nothing.
-spec '>>='(maybe(A), fun( (A) -> maybe(B) )) -> maybe(B).
'>>='({just, X}, Fun) -> Fun(X);
'>>='(nothing, _Fun) -> nothing.
-spec return(A) -> maybe(A).
return(X) -> {just, X}.
-spec fail(any()) -> maybe(_A).
fail(_X) -> nothing.
-spec mzero() -> maybe(_A).
mzero() -> nothing.
-spec mplus(maybe(A), maybe(A)) -> maybe(A).
mplus(nothing, Y) -> Y;
mplus(X, _Y) -> X.