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Variadic fixed-point combinator: Difference between revisions

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Variadic fixed-point combinator (view source)

Revision as of 15:21, 18 March 2024

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(Have removed my own post as I misunderstood the task.)
Tag: Manual revert
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{{out}}
<code>[0,1,2,0,1,2,0,1,2,0,1]</code>
 
=={{header|Java}}==
Note that the yCombinator is defined strictly correctly, that is, its variable name does not appear inside the definition.
<syntaxhighlight lang="java">
import java.util.function.BiFunction;
import java.util.function.Function;
 
public final class VariadicFixedPointCombinator {
 
public static void main(String[] args) {
Function<Integer, Integer> fibonacci = yCombinator(
function -> n -> ( n <= 2 ) ? 1 : function.apply(n - 1) + function.apply(n - 2));
Function<Integer, Integer> factorial = yCombinator(
function -> n -> ( n <= 1 ) ? 1 : n * function.apply(n - 1));
BiFunction<Integer, Integer, Integer> collatz = uncurry(yCombinator(
function -> n -> c -> ( n == 1 ) ?
c : ( n % 2 == 0 ) ?
function.apply(n / 2).apply(c + 1) : function.apply(3 * n + 1).apply(c + 1)
));
BiFunction<Integer, Integer, Integer> ackermann = uncurry(yCombinator(
function -> m -> n -> ( m == 0 ) ?
n + 1 : ( n == 0 ) ?
function.apply(m - 1).apply(1) : function.apply(m - 1).apply(function.apply(m).apply(n - 1))
));
for ( int value = 1; value < 5; value++ ) {
System.out.println("fibonacci(" + value + ") = " + fibonacci.apply(value));
System.out.println("factorial(" + value + ") = " + factorial.apply(value));
System.out.println("collatz(" + value + ") = " + collatz.apply(value, 0));
System.out.println("ackermann(3, " + value + ") = " + ackermann.apply(3, value));
System.out.println();
}
}
private static interface MetaFunction<T> extends Function<MetaFunction<T>, T> { }
private static <T, R> Function<T, R> yCombinator(Function<Function<T, R>, Function<T, R>> function) {
MetaFunction<Function<T, R>> metaFunction = w -> function.apply( x -> w.apply(w).apply(x) );
return metaFunction.apply(metaFunction);
}
private static <T, U, R> BiFunction<T, U, R> uncurry(Function<T, Function<U, R>> function) {
return (x, y) -> function.apply(x).apply(y);
}
 
}
</syntaxhighlight>
{{ out }}
<pre>
fibonacci(1) = 1
factorial(1) = 1
collatz(1) = 0
ackermann(3, 1) = 13
 
fibonacci(2) = 1
factorial(2) = 2
collatz(2) = 1
ackermann(3, 2) = 29
 
fibonacci(3) = 2
factorial(3) = 6
collatz(3) = 7
ackermann(3, 3) = 61
 
fibonacci(4) = 3
factorial(4) = 24
collatz(4) = 2
ackermann(3, 4) = 125
</pre>
 
=={{header|Julia}}==
PSNOW123
894

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