Pack logtalk -- logtalk-3.85.0/examples/metapredicates/SCRIPT.txt

This file is part of Logtalk https://logtalk.org/ SPDX-FileCopyrightText: 1998-2023 Paulo Moura <pmoura@logtalk.org> SPDX-License-Identifier: Apache-2.0

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http://www.apache.org/licenses/LICENSE-2.0

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% start by loading the example and the required library files:

| ?- logtalk_load(metapredicates(loader)). ...

% try the simple meta-predicate definitions from the "goals.lgt" file:

| ?- simple_client::test_whatever.

yes

| ?- simple_client::test_whatever_all.

Hello world! yes

% alternatively:

| ?- simple_client_alt::test_whatever.

yes

| ?- simple_client_alt::test_whatever_all.

Hello world! yes

% note that "user" is a pseudo-object representing the Prolog database; % therefore, the integer comparisons are performed using the standard % Prolog built-in predicates

| ?- sort(user)::sort([3, 1, 4, 2, 9], Sorted).

call: partition([1,4,2,9],3,_358,_359) exit: partition([1,4,2,9],3,[1,2],[4,9]) call: sort([1,2],_740) call: partition([2],1,_967,_968) exit: partition([2],1,[],[2]) call: sort([],_1300) exit: sort([],[]) call: sort([2],_1539) call: partition([],2,_1765,_1766) exit: partition([],2,[],[]) call: sort([],_2093) exit: sort([],[]) call: sort([],_2332) exit: sort([],[]) exit: sort([2],[2]) exit: sort([1,2],[1,2]) call: sort([4,9],_2831) call: partition([9],4,_3058,_3059) exit: partition([9],4,[],[9]) call: sort([],_3391) exit: sort([],[]) call: sort([9],_3630) call: partition([],9,_3856,_3857) exit: partition([],9,[],[]) call: sort([],_4184) exit: sort([],[]) call: sort([],_4423) exit: sort([],[]) exit: sort([9],[9]) exit: sort([4,9],[4,9])

Sorted = [1,2,3,4,9] yes

% test the setof/3 wrapper:

| ?- object::p(L).

L = [1, 2, 3] yes

| ?- object::q(L).

L = [1, 2, 3] yes

% call the meta-predicate apply/2 directly:

| ?- metapreds::test_this.

1, metapreds yes

% send an apply/2 message to self:

| ?- descendant::test_self.

2, descendant yes

% send an apply/2 message from another object:

| ?- test::test_obj.

3, test yes

% use the partition/4 meta-predicate with a predicate defined in the % pseudo-object "user":

| ?- meta::partition(even_integer, [1,2,3,4,5], Included, Excluded).

Included = [2, 4] Excluded = [1, 3, 5] yes

% get a visual illustration of the differences between left and right folds:

| ?- folds::left(Left).

Left = '(((((((((0+1)+2)+3)+4)+5)+6)+7)+8)+9)' yes

| ?- folds::right(Right).

Right = '(1+(2+(3+(4+(5+(6+(7+(8+(9+0)))))))))' yes

% walk a list using left and right folds (note the lambda parameters order):

| ?- meta::fold_left([Y, X, [X|Y]]>>true, [], [1,2,3,4,5,6,7,8,9], R).

R = [9, 8, 7, 6, 5, 4, 3, 2, 1] yes

| ?- meta::fold_right([X, Y, [X|Y]]>>true, [], [1,2,3,4,5,6,7,8,9], R).

R = [1, 2, 3, 4, 5, 6, 7, 8, 9]. yes

% we can compose left folds:

| ?- meta::fold_left([X,Y,Z]>>(Z is X + Y), 0, [1,2,3], Sum).

Sum = 6 yes

| ?- meta::fold_left(meta::fold_left([X,Y,Z]>>(Z is X + Y)), 0, [[1,2,3],[4,5,6]], Sum).

Sum = 21 yes

% use the fold_left/4 meta-predicate with a predicate defined in the % pseudo-object "user":

| ?- meta::fold_left(sum_squares, 0, [1,2,3], Result).

Result = 34 yes

% use the fold_left/4 and fold_right/4 meta-predicates with the atom_concat/3 % Prolog built-in predicate:

| ?- meta::fold_left(atom_concat, 'PREFIX', [abc,def,ghi], Result).

Result = 'PREFIXabcdefghi' yes

| ?- meta::fold_right(atom_concat, 'SUFIX', [abc,def,ghi], Result).

Result = abcdefghiSUFIX yes

% use the fold_left/4 meta-predicate with predicates defined in the object % "predicates":

| ?- meta::fold_left(predicates::sum, 0, [1,2,3,4,5], Result).

Result = 15 yes

| ?- meta::fold_left(predicates::product, 1, [1,2,3,4,5], Result).

Result = 120 yes

| ?- meta::fold_left(predicates::tuple, (0,0), [(1,2), (3,4), (6,4)], Result).

Result = (10, 10) yes

% alternatives to fold_left/4 and fold_right/4 when there isn't an initial value:

| ?- meta::fold_left_1([X,Y,Z]>>(Z is X+Y), [1,2,3,4,5], R). R = 15 yes

| ?- meta::fold_right_1([X,Y,Z]>>(Z is X-Y), [1,2,3,4,5], R). R = 3 yes

| ?- meta::fold_right_1([X,Y,Z]>>(Z is X*Y), [1,2,3,4,5], R). R = 120 yes

% use the scan_left/4 and scan_right/4 meta-predicates with predicates % defined in the object "predicates":

| ?- meta::scan_left(sum_squares, 0, [1,2,3], Result). Result = [0, 1, 5, 34] yes

| ?- meta::scan_right(predicates::sum, 5, [1,2,3,4], Result). Result = [15, 14, 12, 9, 5] yes

% compute a sequence of factorial numbers using a scan of natural numbers % using multiplication:

| ?- meta::scan_left([X,Y,Z]>>(Z is X*Y), 1, [1,2,3,4,5,6], Result). Result = [1, 1, 2, 6, 24, 120, 720] yes

% use the map/2-3 meta-predicates with some Prolog built-in predicates:

| ?- meta::map(integer, [1,2,3,4,5]).

yes

| ?- meta::map(char_code, [a,b,c,d,e], Codes).

Codes = [97, 98, 99, 100, 101] yes

% use the fold_left/4 meta-predicate to calculate Fibonacci numbers:

| ?- fibonacci::nth(10, Fib).

Fib = 55 yes

| ?- fibonacci::nth(Nth, Fib).

Fib = 0 Nth = 0 ? ;

Fib = 1 Nth = 1 ? ;

Fib = 1 Nth = 2 ? ;

Fib = 2 Nth = 3 ? ;

Fib = 3 Nth = 4 ? ;

Fib = 5 Nth = 5 ? ...

% use the map_reduce/5 meta-predicate to give bad news to a company employees:

| ?- company::(company(C1), get_salary(company(C1),S1)).

| ?- company::(company(C1), cut_salary(company(C1), C2), get_salary(C2, S2)).

C1 = [topdept(name('Human Resources'),manager(name('Lisa'),salary(123456)),[]),topdept(name('Development'),manager(name('Anders'),salary(43210)),[subdept(name('Visual Basic'),manager(name('Amanda'),salary(8888)),[]),subdept(name('Visual C#'),manager(name('Erik'),salary(4444)),[])])] C2 = company([topdept(name('Human Resources'),manager(name('Lisa'),salary(61728)),[]),topdept(name('Development'),manager(name('Anders'),salary(21605)),[subdept(name('Visual Basic'),manager(name('Amanda'),salary(4444)),[]),subdept(name('Visual C#'),manager(name('Erik'),salary(2222)),[])])]) S2 = 89999 yes