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<?php |
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/** |
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* For the full copyright and license information, please view |
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* the LICENSE file that was distributed with this source code. |
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*/ |
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declare(strict_types=1); |
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namespace loophp\churchencoding; |
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use Closure; |
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use loophp\combinator\Combinators; |
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/** |
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* Class Numeral. |
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* |
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* phpcs:disable Generic.Files.LineLength.TooLong |
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*/ |
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final class Numeral |
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{ |
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public static function eight(): Closure |
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{ |
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return self::succ()(self::seven()); |
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} |
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public static function exponentiation(): Closure |
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{ |
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return Combinators::T(); |
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} |
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public static function five(): Closure |
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{ |
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return self::succ()(self::four()); |
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} |
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public static function four(): Closure |
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{ |
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return self::succ()(self::three()); |
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} |
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public static function minus(): Closure |
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{ |
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return Combinators::V()(self::pred()); |
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} |
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public static function multiply(): Closure |
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{ |
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return Combinators::B(); |
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} |
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public static function nine(): Closure |
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{ |
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return self::succ()(self::eight()); |
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} |
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public static function one(): Closure |
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{ |
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return self::succ()(self::zero()); |
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} |
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public static function plus(): Closure |
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{ |
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return static fn (callable $a): Closure => static fn (callable $b): Closure => static fn (callable $c): Closure => Combinators::B()($a($c))($b($c)); |
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} |
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public static function pred(): Closure |
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{ |
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return static fn (callable $a): Closure => static fn (callable $b): Closure => static fn ($c) => $a(static fn (callable $d): Closure => static fn (callable $e) => $e($d($b)))(static fn () => $c)(Combinators::I()); |
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} |
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public static function seven(): Closure |
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{ |
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return self::succ()(self::six()); |
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} |
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public static function six(): Closure |
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{ |
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return self::succ()(self::five()); |
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} |
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public static function succ(): Closure |
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{ |
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return static fn (callable $n): Closure => static fn (callable $f): Closure => Combinators::B()($f)($n($f)); |
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} |
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public static function three(): Closure |
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{ |
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return self::succ()(self::two()); |
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} |
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public static function toInt(callable $numeral): int |
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{ |
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return $numeral(static fn (int $n): int => $n + 1)(0); |
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} |
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public static function toNumeral(int $n): Closure |
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{ |
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return 0 === $n ? |
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Numeral::zero() : |
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Numeral::succ()(Numeral::toNumeral($n - 1)); |
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} |
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public static function two(): Closure |
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{ |
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return self::succ()(self::one()); |
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} |
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public static function zero(): Closure |
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{ |
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return static fn (): Closure => Combinators::I(); |
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} |
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} |
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loophp /
church-encoding
