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G-Apomorphism
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‎src/main/java/com/jnape/palatable/lambda/recursionschemes/builtin/GApomorphism.java

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package com.jnape.palatable.lambda.recursionschemes.builtin;
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import com.jnape.palatable.lambda.adt.coproduct.CoProduct2;
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import com.jnape.palatable.lambda.functions.Fn1;
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import com.jnape.palatable.lambda.functions.Fn2;
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import com.jnape.palatable.lambda.functions.Fn3;
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import com.jnape.palatable.lambda.functor.Functor;
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import com.jnape.palatable.lambda.recursionschemes.Coalgebra;
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import com.jnape.palatable.lambda.recursionschemes.Fix;
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import java.util.function.Function;
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import static com.jnape.palatable.lambda.recursionschemes.Fix.fix;
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import static com.jnape.palatable.lambda.recursionschemes.builtin.Anamorphism.ana;
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public final class GApomorphism<A, B, F extends Functor, FT extends Functor<CoProduct2<A, B>, F>, FB extends Functor<B, F>>
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implements Fn3<Function<A, FT>, Coalgebra<B, FB>, A, Fix<F, Functor<Fix<F, ?>, F>>> {
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private static final GApomorphism INSTANCE = new GApomorphism();
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private GApomorphism() {
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}
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@Override
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public Fix<F, Functor<Fix<F, ?>, F>> apply(Function<A, FT> fn, Coalgebra<B, FB> coalgebra, A a) {
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return fix(fn.apply(a).fmap((Function<CoProduct2<A, B>, Fix<F, Functor<Fix<F, ?>, F>>>)
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cp2 -> cp2.match(gApo(fn, coalgebra), ana(coalgebra))));
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}
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@SuppressWarnings("unchecked")
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public static <A, B, F extends Functor, FT extends Functor<CoProduct2<A, B>, F>, FB extends Functor<B, F>> GApomorphism<A, B, F, FT, FB> gApo() {
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return INSTANCE;
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}
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public static <A, B, F extends Functor, FT extends Functor<CoProduct2<A, B>, F>, FB extends Functor<B, F>> Fn2<Coalgebra<B, FB>, A, Fix<F, Functor<Fix<F, ?>, F>>> gApo(
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Function<A, FT> fn) {
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return GApomorphism.<A, B, F, FT, FB>gApo().apply(fn);
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}
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public static <A, B, F extends Functor, FT extends Functor<CoProduct2<A, B>, F>, FB extends Functor<B, F>> Fn1<A, Fix<F, Functor<Fix<F, ?>, F>>> gApo(
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Function<A, FT> fn, Coalgebra<B, FB> coalgebra) {
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return GApomorphism.<A, B, F, FT, FB>gApo(fn).apply(coalgebra);
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}
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public static <A, B, F extends Functor, FT extends Functor<CoProduct2<A, B>, F>, FB extends Functor<B, F>> Fix<F, Functor<Fix<F, ?>, F>> gApo(
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Function<A, FT> fn, Coalgebra<B, FB> coalgebra, A a) {
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return gApo(fn, coalgebra).apply(a);
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}
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}

‎src/test/java/com/jnape/palatable/lambda/recursionschemes/builtin/ApomorphismTest.java

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import com.jnape.palatable.lambda.adt.coproduct.CoProduct2;
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import com.jnape.palatable.lambda.recursionschemes.Fix;
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import org.junit.Test;
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import testsupport.recursion.ListF;
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import testsupport.recursion.NatF;
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import java.util.function.Function;
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import static com.jnape.palatable.lambda.recursionschemes.Fix.fix;
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import static com.jnape.palatable.lambda.recursionschemes.builtin.Apomorphism.apo;
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import static org.junit.Assert.assertEquals;
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import static testsupport.recursion.ListF.cons;
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import static testsupport.recursion.ListF.nil;
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public class ApomorphismTest {
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@Test
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public void unfoldingToGreatestFixedPointWithShortCircuit() {
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Function<Integer, NatF<CoProduct2<Integer, Fix<NatF, NatF<Fix<NatF, ?>>>>>> unfold =
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Function<Integer, NatF<CoProduct2<Integer, Fix<NatF, NatF<Fix<NatF, ?>>>>>> nats =
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x -> NatF.s(x < 3 ? a(x + 1) : b(fix(NatF.z())));
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assertEquals(Fix.<NatF, NatF<Fix<NatF, ?>>>fix(NatF.s(fix(NatF.z()))), apo(nats, 3));
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assertEquals(Fix.<NatF, NatF<Fix<NatF, ?>>>fix(NatF.s(fix(NatF.s(fix(NatF.s(fix(NatF.z()))))))), apo(nats, 1));
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assertEquals(Fix.<NatF, NatF<Fix<NatF, ?>>>fix(NatF.s(fix(NatF.s(fix(NatF.s(fix(NatF.z()))))))), apo(unfold, 1));
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Function<Integer, ListF<String, CoProduct2<Integer, Fix<ListF<String, ?>, ListF<String, Fix<ListF<String, ?>, ?>>>>>> unfold =
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x -> cons("<" + x + ">", x < 3 ? a(x + 1) : b(fix(nil())));
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assertEquals(Fix.<ListF<String, ?>, ListF<String, Fix<ListF<String, ?>, ?>>>fix(cons("<1>", fix(cons("<2>", fix(cons("<3>", fix(nil()))))))), apo(unfold, 1));
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assertEquals(Fix.<ListF<String, ?>, ListF<String, Fix<ListF<String, ?>, ?>>>fix(cons("<3>", fix(nil()))), apo(unfold, 3));
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}
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}

‎src/test/java/com/jnape/palatable/lambda/recursionschemes/builtin/GApomorphismTest.java

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package com.jnape.palatable.lambda.recursionschemes.builtin;
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import com.jnape.palatable.lambda.adt.coproduct.CoProduct2;
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import com.jnape.palatable.lambda.recursionschemes.Fix;
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import org.junit.Test;
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import testsupport.recursion.ListF;
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import testsupport.recursion.NatF;
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import java.util.function.Function;
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import static com.jnape.palatable.lambda.adt.choice.Choice2.a;
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import static com.jnape.palatable.lambda.adt.choice.Choice2.b;
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import static com.jnape.palatable.lambda.recursionschemes.Fix.fix;
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import static com.jnape.palatable.lambda.recursionschemes.builtin.Apomorphism.apo;
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import static com.jnape.palatable.lambda.recursionschemes.builtin.GApomorphism.gApo;
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import static org.junit.Assert.assertEquals;
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import static testsupport.recursion.ListF.cons;
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import static testsupport.recursion.ListF.nil;
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public class GApomorphismTest {
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@Test
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public void unfoldingToGreatestFixedPointWithShortCircuitAndCoalgebra() {
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Function<Integer, NatF<CoProduct2<Integer, Fix<NatF, NatF<Fix<NatF, ?>>>>>> nats =
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x -> NatF.s(x < 3 ? a(x + 1) : b(fix(NatF.z())));
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assertEquals(apo(nats, 3), gApo(nats, __ -> NatF.z(), 3));
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assertEquals(apo(nats, 1), gApo(nats, __ -> NatF.z(), 1));
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Function<Integer, ListF<String, CoProduct2<Integer, Fix<ListF<String, ?>, ListF<String, Fix<ListF<String, ?>, ?>>>>>> unfold =
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x -> cons("<" + x + ">", x < 3 ? a(x + 1) : b(fix(nil())));
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assertEquals(apo(unfold, 1), gApo(unfold, __ -> ListF.nil(), 1));
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assertEquals(apo(unfold, 3), gApo(unfold, __ -> ListF.nil(), 3));
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}
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}

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