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Lines changed: 96 additions & 36 deletions

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src/main/java/fix/Coalgebra.java renamed to src/main/java/com/jnape/palatable/lambda/recursionschemes/Coalgebra.java

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@@ -1,4 +1,4 @@
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package fix;
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package com.jnape.palatable.lambda.recursionschemes;
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import com.jnape.palatable.lambda.functions.Fn1;
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import com.jnape.palatable.lambda.functor.Functor;

‎src/main/java/com/jnape/palatable/lambda/recursionschemes/Cofree.java‎

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package com.jnape.palatable.lambda.recursionschemes;
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import com.jnape.palatable.lambda.adt.hlist.Tuple2;
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import com.jnape.palatable.lambda.functor.Functor;
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import static com.jnape.palatable.lambda.adt.hlist.HList.tuple;
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public interface Cofree<A, F extends Functor, CofreeF extends Functor<?, F>> {
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Tuple2<A, CofreeF> uncofree();
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static <A, F extends Functor, CofreeF extends Functor<? extends Cofree<A, F, ?>, F>> Cofree<A, F, CofreeF> coFree(
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A a, CofreeF f) {
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return () -> tuple(a, f);
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}
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}

‎src/main/java/com/jnape/palatable/lambda/recursionschemes/Free.java‎

Lines changed: 38 additions & 30 deletions
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@@ -1,14 +1,11 @@
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package com.jnape.palatable.lambda.recursionschemes;
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3-
import com.jnape.palatable.lambda.adt.choice.Choice2;
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import com.jnape.palatable.lambda.adt.coproduct.CoProduct2;
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import com.jnape.palatable.lambda.functor.Functor;
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import fix.Coalgebra;
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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.functions.builtin.fn1.Constantly.constantly;
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import static com.jnape.palatable.lambda.recursionschemes.builtin.Anamorphism.ana;
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/**
@@ -25,12 +22,7 @@
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* @param <F> the functor unification type
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* @param <FreeF> the type corresponding to the functor that wraps Free
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*/
28-
public final class Free<A, F extends Functor, FreeF extends Functor<?, F>> implements CoProduct2<A, FreeF> {
29-
private final Choice2<A, FreeF> choice;
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private Free(Choice2<A, FreeF> choice) {
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this.choice = choice;
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}
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public interface Free<A, F extends Functor, FreeF extends Functor<?, F>> extends CoProduct2<A, FreeF> {
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/**
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* Given a {@link Coalgebra}, recursively fold this <code>Free</code> into a {@link Fix}. Note that this is only
@@ -41,27 +33,12 @@ private Free(Choice2<A, FreeF> choice) {
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* @return the fix version of this free
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*/
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@SuppressWarnings("unchecked")
44-
public <FA extends Functor<A, F>> Fix<F, ? extends Functor<? extends Fix<F, ?>, F>> fix(
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default <FA extends Functor<A, F>> Fix<F, ? extends Functor<? extends Fix<F, ?>, F>> fix(
4537
Coalgebra<A, FA> coalgebra) {
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return match(a -> ana(coalgebra, a),
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freeF -> Fix.fix(freeF.fmap(x1 -> ((Free<A, F, FreeF>) x1).fix(coalgebra))));
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}
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@Override
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public <R> R match(Function<? super A, ? extends R> aFn, Function<? super FreeF, ? extends R> bFn) {
52-
return choice.match(aFn, bFn);
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}
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@Override
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public boolean equals(Object other) {
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return other instanceof Free && choice.equals(((Free) other).choice);
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}
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@Override
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public int hashCode() {
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return choice.hashCode();
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}
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/**
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* The recursive expression in free construction, using a functor.
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*
@@ -71,9 +48,24 @@ public int hashCode() {
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* @param <FreeF> the type corresponding to the functor that wraps Free
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* @return an instance of Free over this functor
7350
*/
74-
public static <A, F extends Functor, FreeF extends Functor<? extends Free<A, F, ?>, F>> Free<A, F, FreeF> free(
51+
static <A, F extends Functor, FreeF extends Functor<? extends Free<A, F, ?>, F>> Free<A, F, FreeF> free(
7552
FreeF f) {
76-
return new Free<>(b(f));
53+
return new Free<A, F, FreeF>() {
54+
@Override
55+
public <R> R match(Function<? super A, ? extends R> aFn, Function<? super FreeF, ? extends R> bFn) {
56+
return bFn.apply(f);
57+
}
58+
59+
@Override
60+
public boolean equals(Object other) {
61+
return other instanceof Free && ((Free<?, ?, ?>) other).match(constantly(false), f::equals);
62+
}
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@Override
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public int hashCode() {
66+
return 31 + f.hashCode();
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}
68+
};
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}
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/**
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8577
* @param <FreeF> the type corresponding to the functor that wraps Free
8678
* @return an instance of Free over this value
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*/
88-
public static <A, F extends Functor, FreeF extends Functor<?, F>> Free<A, F, FreeF> pure(A a) {
89-
return new Free<>(a(a));
80+
static <A, F extends Functor, FreeF extends Functor<?, F>> Free<A, F, FreeF> pure(A a) {
81+
return new Free<A, F, FreeF>() {
82+
@Override
83+
public <R> R match(Function<? super A, ? extends R> aFn, Function<? super FreeF, ? extends R> bFn) {
84+
return aFn.apply(a);
85+
}
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87+
@Override
88+
public boolean equals(Object other) {
89+
return other instanceof Free && ((Free<?, ?, ?>) other).match(a::equals, constantly(false));
90+
}
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@Override
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public int hashCode() {
94+
return 31 + a.hashCode();
95+
}
96+
};
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9098
}
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}

‎src/main/java/com/jnape/palatable/lambda/recursionschemes/builtin/Anamorphism.java‎

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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.functor.Functor;
6+
import com.jnape.palatable.lambda.recursionschemes.Coalgebra;
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import com.jnape.palatable.lambda.recursionschemes.Fix;
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import com.jnape.palatable.lambda.recursionschemes.Thunk;
8-
import fix.Coalgebra;
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1010
import static com.jnape.palatable.lambda.recursionschemes.Fix.fix;
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‎src/main/java/com/jnape/palatable/lambda/recursionschemes/builtin/Hylomorphism.java‎

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@@ -5,7 +5,7 @@
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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.Algebra;
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import fix.Coalgebra;
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import com.jnape.palatable.lambda.recursionschemes.Coalgebra;
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1010
import static com.jnape.palatable.lambda.recursionschemes.builtin.Anamorphism.ana;
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import static com.jnape.palatable.lambda.recursionschemes.builtin.Catamorphism.cata;

‎src/test/java/com/jnape/palatable/lambda/recursionschemes/FreeTest.java‎

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package com.jnape.palatable.lambda.recursionschemes;
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3-
import fix.Coalgebra;
43
import org.junit.Test;
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import testsupport.recursion.ListF;
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import testsupport.recursion.NatF;

‎src/test/java/com/jnape/palatable/lambda/recursionschemes/Spike.java‎

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package com.jnape.palatable.lambda.recursionschemes;
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import com.jnape.palatable.lambda.adt.hlist.Tuple2;
4+
import com.jnape.palatable.lambda.functor.Functor;
5+
import testsupport.recursion.NatF;
6+
7+
import java.util.function.Function;
8+
9+
import static com.jnape.palatable.lambda.adt.hlist.HList.tuple;
10+
import static com.jnape.palatable.lambda.functions.builtin.fn1.Constantly.constantly;
11+
import static com.jnape.palatable.lambda.recursionschemes.Fix.fix;
12+
import static com.jnape.palatable.lambda.recursionschemes.builtin.Catamorphism.cata;
13+
import static testsupport.recursion.NatF.s;
14+
import static testsupport.recursion.NatF.z;
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16+
public class Spike {
17+
18+
@SuppressWarnings("unchecked")
19+
public static <A, F extends Functor, Unfixed extends Functor<? extends Fix<F, ?>, F>> A para(
20+
Function<Functor<Tuple2<Fix<F, Unfixed>, A>, F>, A> fn,
21+
Fix<F, Unfixed> fixed) {
22+
Algebra<Functor<Tuple2<Fix<F, Unfixed>, A>, F>, Tuple2<Fix<F, Unfixed>, A>> alg =
23+
f -> tuple(fix((Unfixed) f.fmap(Tuple2::_1)), fn.apply(f));
24+
return cata(alg, fixed)._2();
25+
}
26+
27+
public static void main(String[] args) {
28+
Function<Functor<Tuple2<Fix<NatF, NatF<Fix<NatF, ?>>>, Integer>, NatF>, Integer> x = new Function<Functor<Tuple2<Fix<NatF, NatF<Fix<NatF, ?>>>, Integer>, NatF>, Integer>() {
29+
@Override
30+
public Integer apply(Functor<Tuple2<Fix<NatF, NatF<Fix<NatF, ?>>>, Integer>, NatF> fnat) {
31+
NatF<Tuple2<Fix<NatF, NatF<Fix<NatF, ?>>>, Integer>> xn = (NatF<Tuple2<Fix<NatF, NatF<Fix<NatF, ?>>>, Integer>>) fnat;
32+
return xn.match(constantly(0), s -> s.carrier()._2() + 1);
33+
}
34+
};
35+
System.out.println(para(x, fix(s(fix(z())))));
36+
}
37+
}

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

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import com.jnape.palatable.lambda.recursionschemes.Algebra;
44
import com.jnape.palatable.lambda.recursionschemes.Fix;
5-
import fix.Coalgebra;
5+
import com.jnape.palatable.lambda.recursionschemes.Coalgebra;
66
import org.junit.Test;
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import testsupport.recursion.ListF;
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import testsupport.recursion.NatF;

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

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package com.jnape.palatable.lambda.recursionschemes.builtin;
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import com.jnape.palatable.lambda.recursionschemes.Algebra;
4-
import fix.Coalgebra;
4+
import com.jnape.palatable.lambda.recursionschemes.Coalgebra;
55
import org.junit.Test;
66
import testsupport.recursion.ListF;
77
import testsupport.recursion.NatF;

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