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lambdas.lgt
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lambdas.lgt
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
% This file is part of Logtalk <https://logtalk.org/>
% Copyright 1998-2020 Paulo Moura <pmoura@logtalk.org>
%
% Licensed under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0
%
% Unless required by applicable law or agreed to in writing, software
% distributed under the License is distributed on an "AS IS" BASIS,
% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
% See the License for the specific language governing permissions and
% limitations under the License.
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
:- object(countries).
:- info([
version is 1:0:0,
date is 2009-11-28,
author is 'Paulo Moura',
comment is 'Simple example of using lambda expressions to simplify setof/3 and similar calls.'
]).
:- public(currencies_wrong/1).
currencies_wrong(Currencies) :-
setof(Currency, country(_, _, _, Currency), Currencies).
:- public(currencies_no_lambda/1).
currencies_no_lambda(Currencies) :-
setof(Currency, Country^Capital^Population^country(Country, Capital, Population, Currency), Currencies).
% adapted from a Ulrich Neumerkel's lambda proposal example
:- public(currencies_lambda/1).
currencies_lambda(Currencies) :-
setof(Currency, {Currency}/country(_, _, _, Currency), Currencies).
% country(Country, Capital, Population, Currency)
country(portugal, lisbon, 10, euro).
country(spain, madrid, 46, euro).
country(england, london, 51, pound_sterling).
country(malaysia, kuala_lumpur, 28, ringgit).
country(iraq, baghdad, 31, dinar).
country(tunisia, tunis, 10, dinar).
:- end_object.
:- object(sigma).
:- info([
version is 1:0:0,
author is 'Artur Miguel Dias',
date is 2009-12-04,
comment is 'Generic sum predicate for testing lambda expressions.'
]).
% note that this is simple an example of using lambda expressions; Logtalk
% already includes a fold_left/4 predicate in its library that could
% easily be used for performing the same computations
:- public(sum/4).
:- meta_predicate(sum(2, *, *, *)).
:- meta_predicate(sum(2, *, *, *, *)).
sum(Closure, Inf, Sup, Result) :-
sum(Closure, Inf, Sup, 0, Result).
sum(Closure, Inf, Sup, Acc, Result) :-
( Inf =< Sup ->
call(Closure, Inf, Sum),
Acc2 is Acc + Sum,
Next is Inf + 1,
sum(Closure, Next, Sup, Acc2, Result)
; Result = Acc
).
:- end_object.
:- object(misc).
:- info([
version is 1:3:0,
date is 2019-08-17,
author is 'Paulo Moura',
comment is 'Some miscellaneous tests for lambda expressions collected from public forums.'
]).
% adapted from a Richard O'Keefe example
:- public(common_prefix/3).
% avoid spurious warning about missing meta_predicate/1 directive
:- meta_predicate(common_prefix(*, *, *)).
common_prefix(Front, Xs, Ys) :-
meta::map({Front}/(list::append(Front)), Xs, Ys).
% an alternative definition
%
%:- uses(meta, [map/3]).
%:- uses(list, [append/3]).
%
%common_prefix(Front, Xs, Ys) :-
% map({Front}/append(Front), Xs, Ys).
% adapted from a Ulrich Neumerkel's lambda proposal example
:- public(call_n/0).
call_n :-
f(X, Y),
write('This test should print '), write(f(X, Y)), write(' in all lines:'), nl,
call(f, A1, A2), write(f(A1, A2)), nl,
call([X1]>>f(X1), B1, B2), write(f(B1, B2)), nl,
call([X2,Y2]>>f(X2,Y2), C1, C2), write(f(C1, C2)), nl,
call([X3]>>({X3}/[Y3]>>f(X3,Y3)), D1, D2), write(f(D1, D2)), nl,
call(call(f, E1), E2), write(f(E1, E2)), nl,
call(f(F1), F2), write(f(F1, F2)), nl.
f(x, y).
% use ()'s in order to avoid a XSB parser error
:- public((local)/0).
local :-
integer::sequence(1, 100, List),
meta::map([X]>>less(0,X),List).
less(X, Y) :-
X < Y.
:- end_object.
:- if((
current_logtalk_flag(prolog_dialect, Dialect),
(Dialect == b; Dialect == swi; Dialect == xsb; Dialect == yap)
)).
:- object(lambda_benchmarks).
:- public([bench1/0, bench2/0]).
% the time/1 predicate is a library predicate in SWI-Prolog
% and a built-in predicate in B-Prolog, XSB and YAP
:- if(current_logtalk_flag(prolog_dialect, swi)).
:- use_module(prolog_statistics, [time/1]).
:- endif.
:- uses(integer, [sequence/3]).
:- uses(meta, [map/2, map/3]).
bench1 :-
sequence(1, 100000, List),
write('Using map/2 with a closure for testing less(0, X) with X in [1..100000]: '), nl,
time(map(less(0), List)),
write('Using map/2 with a lambda for testing less(0, X) with X in [1..100000]: '), nl,
time(map([X]>>less(0,X), List)).
less(X, Y) :-
X < Y.
% the second benchmark is based on code posted by Jan Wielemaker in the SWI-Prolog mailing list:
bench2 :-
sequence(1, 100000, List),
( ( write('Adding 1 to every integer in the list [1..100000] using a local add1/2 predicate:'), nl,
time(add1(List, _))
; write('Adding 1 to every integer in the list [1..100000] using map/3 with the integer::plus/3 predicate:'), nl,
time(sum(List, _))
; write('Adding 1 to every integer in the list [1..100000] using map/3 with a lambda argument with a is/2 goal:'), nl,
time(map([X,Y]>>{Y is X+1}, List, _))
),
fail
; true
).
sum(List1, List2) :-
map(integer::plus(1), List1, List2).
add1([], []).
add1([H0| T0], [H| T]) :-
H is H0 + 1,
add1(T0, T).
:- end_object.
:- endif.