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LambdaMap, lambda extension type for j.u.Map
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‎CHANGELOG.md

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@@ -12,6 +12,8 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/).
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- `Product2-8` interfaces, representing general product types
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- `Union`, a semigroup that behaves like a lazy set union on `Iterable`s
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- `Difference`, a semigroup that behaves like a partially lazy set difference on `Iterable`s
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- `LambdaMap`, extension point for `j.u.Map`, similar to `LambdaIterable`
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- `Sequence#sequence` overloads for `j.u.Map` that traverse via intermediate `LambdaMap` instances
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### Changed
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- `Tuple2-8` now implement `Product2-8`

‎src/main/java/com/jnape/palatable/lambda/functions/builtin/fn2/Sequence.java

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@@ -4,8 +4,10 @@
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import com.jnape.palatable.lambda.functions.Fn2;
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import com.jnape.palatable.lambda.functor.Applicative;
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import com.jnape.palatable.lambda.traversable.LambdaIterable;
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import com.jnape.palatable.lambda.traversable.LambdaMap;
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import com.jnape.palatable.lambda.traversable.Traversable;
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import java.util.Map;
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import java.util.function.Function;
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import static com.jnape.palatable.lambda.functions.builtin.fn1.Id.id;
@@ -83,4 +85,17 @@ TravApp extends Traversable<AppA, Trav>> AppTrav sequence(TravApp traversable,
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AppIterable sequence(IterableApp iterableApp, Function<Iterable<A>, ? extends AppIterable> pure) {
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return Sequence.<A, App, AppA, AppIterable, IterableApp>sequence(iterableApp).apply(pure);
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}
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@SuppressWarnings({"unchecked", "RedundantTypeArguments"})
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public static <A, B, App extends Applicative, AppB extends Applicative<B, App>, AppMap extends Applicative<Map<A, B>, App>, MapApp extends Map<A, AppB>>
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Fn1<Function<Map<A, B>, ? extends AppMap>, AppMap> sequence(MapApp mapApp) {
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return pure -> (AppMap) Sequence.<B, App, LambdaMap<A, ?>, LambdaMap<A, B>, AppB, Applicative<LambdaMap<A, B>, App>, LambdaMap<A, AppB>>sequence(
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LambdaMap.wrap(mapApp), x -> pure.apply(x.unwrap()).fmap(LambdaMap::wrap))
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.fmap(LambdaMap::unwrap);
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}
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public static <A, B, App extends Applicative, AppB extends Applicative<B, App>, AppMap extends Applicative<Map<A, B>, App>, MapApp extends Map<A, AppB>>
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AppMap sequence(MapApp mapApp, Function<Map<A, B>, ? extends AppMap> pure) {
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return Sequence.<A, B, App, AppB, AppMap, MapApp>sequence(mapApp).apply(pure);
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}
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}

‎src/main/java/com/jnape/palatable/lambda/monoid/Difference.java

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@@ -22,7 +22,6 @@ public Iterable<A> identity() {
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return Collections::emptyIterator;
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}
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@Override
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public Iterable<A> apply(Iterable<A> xs, Iterable<A> ys) {
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return () -> {

‎src/main/java/com/jnape/palatable/lambda/traversable/LambdaIterable.java

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@@ -8,20 +8,17 @@
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import java.util.function.Function;
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import static com.jnape.palatable.lambda.functions.builtin.fn1.Flatten.flatten;
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import static com.jnape.palatable.lambda.functions.builtin.fn2.CartesianProduct.cartesianProduct;
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import static com.jnape.palatable.lambda.functions.builtin.fn2.Cons.cons;
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import static com.jnape.palatable.lambda.functions.builtin.fn2.Into.into;
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import static com.jnape.palatable.lambda.functions.builtin.fn2.Map.map;
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import static com.jnape.palatable.lambda.functions.builtin.fn3.FoldRight.foldRight;
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import static java.util.Collections.emptyList;
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import static java.util.Collections.singleton;
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/**
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* Wrap an {@link Iterable} in a {@link Traversable} such that {@link Traversable#traverse(Function, Function)} applies
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* its computation against each element of the wrapped {@link Iterable}. Returns the result of <code>pure</code> if the
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* wrapped {@link Iterable} is empty.
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* Extension point for {@link Iterable} to adapt lambda core types like {@link Monad} and {@link Traversable}.
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*
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* @param <A> the Iterable element type
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* @param <A> the {@link Iterable} element type
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* @see LambdaMap
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*/
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public final class LambdaIterable<A> implements Monad<A, LambdaIterable>, Traversable<A, LambdaIterable> {
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private final Iterable<A> as;
@@ -34,7 +31,7 @@ private LambdaIterable(Iterable<? extends A> as) {
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/**
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* Unwrap the underlying {@link Iterable}.
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*
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* @return the wrapped Iterable
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* @return the wrapped {@link Iterable}
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*/
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public Iterable<A> unwrap() {
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return as;
@@ -61,10 +58,8 @@ public <B> LambdaIterable<B> pure(B b) {
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* @return the zipped LambdaIterable
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*/
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@Override
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@SuppressWarnings("Convert2MethodRef")
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public <B> LambdaIterable<B> zip(Applicative<Function<? super A, ? extends B>, LambdaIterable> appFn) {
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return wrap(map(into((f, x) -> f.apply(x)),
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cartesianProduct(appFn.<LambdaIterable<Function<? super A, ? extends B>>>coerce().unwrap(), as)));
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return Monad.super.zip(appFn).coerce();
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}
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@Override
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* Construct an empty {@link LambdaIterable} by wrapping {@link java.util.Collections#emptyList()}.
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*
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* @param <A> the Iterable element type
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* @return a {@link LambdaIterable} wrapping Collections.emptyList()
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* @return an empty {@link LambdaIterable}
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*/
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public static <A> LambdaIterable<A> empty() {
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return wrap(emptyList());

‎src/main/java/com/jnape/palatable/lambda/traversable/LambdaMap.java

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package com.jnape.palatable.lambda.traversable;
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import com.jnape.palatable.lambda.functions.Fn2;
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import com.jnape.palatable.lambda.functor.Applicative;
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import com.jnape.palatable.lambda.functor.Functor;
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import java.util.Collections;
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import java.util.HashMap;
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import java.util.Map;
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import java.util.Objects;
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import java.util.function.Function;
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import static com.jnape.palatable.lambda.adt.hlist.HList.tuple;
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import static com.jnape.palatable.lambda.functions.builtin.fn2.Into.into;
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import static com.jnape.palatable.lambda.functions.builtin.fn2.Map.map;
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import static com.jnape.palatable.lambda.functions.builtin.fn2.ToMap.toMap;
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import static com.jnape.palatable.lambda.functions.builtin.fn3.FoldLeft.foldLeft;
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import static java.util.Collections.emptyMap;
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/**
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* Extension point for {@link Map} to adapt lambda core types like {@link Functor} and {@link Traversable}.
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*
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* @param <A> the {@link Map} element type
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* @see LambdaIterable
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*/
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public final class LambdaMap<A, B> implements Functor<B, LambdaMap<A, ?>>, Traversable<B, LambdaMap<A, ?>> {
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private final Map<A, B> map;
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private LambdaMap(Map<A, B> map) {
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this.map = map;
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}
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/**
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* Unwrap the underlying {@link Map}.
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*
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* @return the wrapped {@link Map}
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*/
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public Map<A, B> unwrap() {
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return map;
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}
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@Override
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public <C> LambdaMap<A, C> fmap(Function<? super B, ? extends C> fn) {
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return wrap(toMap(HashMap::new, map(entry -> tuple(entry.getKey(), fn.apply(entry.getValue())), map.entrySet())));
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}
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@Override
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@SuppressWarnings("unchecked")
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public <C, App extends Applicative, TravC extends Traversable<C, LambdaMap<A, ?>>, AppC extends Applicative<C, App>, AppTrav extends Applicative<TravC, App>> AppTrav traverse(
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Function<? super B, ? extends AppC> fn, Function<? super TravC, ? extends AppTrav> pure) {
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return foldLeft(Fn2.<AppTrav, Map.Entry<A, AppC>, AppTrav>fn2(appTrav -> into((k, appV) -> (AppTrav) appTrav.<TravC>zip(appV.fmap(v -> m -> {
52+
((LambdaMap<A, C>) m).unwrap().put(k, v);
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return (TravC) m;
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})))).toBiFunction(),
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pure.apply((TravC) LambdaMap.<A, C>wrap(new HashMap<>())),
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this.<AppC>fmap(fn).unwrap().entrySet());
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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 LambdaMap && Objects.equals(map, ((LambdaMap) other).map);
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}
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@Override
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public int hashCode() {
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return Objects.hash(map);
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}
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@Override
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public String toString() {
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return "LambdaMap{map=" + map + '}';
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}
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/**
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* Wrap a {@link Map} in a {@link LambdaMap}.
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*
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* @param map the {@link Map}
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* @param <A> the key type
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* @param <B> the value type
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* @return the {@link Map} wrapped in a {@link LambdaMap}
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*/
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public static <A, B> LambdaMap<A, B> wrap(Map<A, B> map) {
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return new LambdaMap<>(map);
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}
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/**
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* Construct an empty {@link LambdaMap} by wrapping {@link Collections#emptyMap()}
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*
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* @param <A> the key type
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* @param <B> the value type
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* @return an empty {@link LambdaMap}
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*/
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public static <A, B> LambdaMap<A, B> empty() {
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return wrap(emptyMap());
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}
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}

‎src/test/java/com/jnape/palatable/lambda/functions/builtin/fn2/SequenceTest.java

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@@ -13,6 +13,7 @@
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import static com.jnape.palatable.lambda.functions.builtin.fn1.Id.id;
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import static com.jnape.palatable.lambda.functions.builtin.fn2.Sequence.sequence;
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import static java.util.Arrays.asList;
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import static java.util.Collections.singletonMap;
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import static org.junit.Assert.assertEquals;
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import static org.junit.Assert.assertThat;
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import static testsupport.matchers.IterableMatcher.iterates;
@@ -49,6 +50,12 @@ public void iterableSpecialization() {
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iterates(1, 2));
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}
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@Test
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public void mapSpecialization() {
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assertEquals(right(singletonMap("foo", 1)),
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sequence(singletonMap("foo", right(1)), Either::right));
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}
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@Test
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public void compilation() {
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Either<String, Maybe<Integer>> a = sequence(just(right(1)), Either::right);

‎src/test/java/com/jnape/palatable/lambda/traversable/LambdaMapTest.java

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package com.jnape.palatable.lambda.traversable;
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import com.jnape.palatable.traitor.annotations.TestTraits;
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import com.jnape.palatable.traitor.framework.Subjects;
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import com.jnape.palatable.traitor.runners.Traits;
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import org.junit.runner.RunWith;
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import testsupport.traits.FunctorLaws;
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import testsupport.traits.TraversableLaws;
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import java.util.HashMap;
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import static com.jnape.palatable.traitor.framework.Subjects.subjects;
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import static java.util.Collections.singletonMap;
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@RunWith(Traits.class)
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public class LambdaMapTest {
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@TestTraits({FunctorLaws.class, TraversableLaws.class})
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public Subjects<LambdaMap<Integer, String>> testSubject() {
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return subjects(LambdaMap.empty(),
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LambdaMap.wrap(singletonMap(1, "foo")),
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LambdaMap.wrap(new HashMap<Integer, String>() {{
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put(1, "foo");
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put(2, "bar");
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put(3, "baz");
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}}));
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}
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}

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