IterableLens#mapping, an Iso for mapping Iterables

jnape · jnape · commit 629000a14976 · 2018-05-18T18:44:37.000-05:00
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -4,6 +4,9 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/).
 
 ## [Unreleased]
+### Added
+- `IterableLens#mapping`, an `Iso` that maps values
+
 ### Changed
 - `TypeSafeKey.Simple` now has a default `#apply` implementation
 
diff --git a/src/main/java/com/jnape/palatable/lambda/lens/lenses/IterableLens.java b/src/main/java/com/jnape/palatable/lambda/lens/lenses/IterableLens.java
@@ -3,12 +3,16 @@
 import com.jnape.palatable.lambda.adt.Maybe;
 import com.jnape.palatable.lambda.functions.builtin.fn1.Head;
 import com.jnape.palatable.lambda.functions.builtin.fn1.Tail;
+import com.jnape.palatable.lambda.lens.Iso;
 import com.jnape.palatable.lambda.lens.Lens;
 
 import static com.jnape.palatable.lambda.functions.Fn2.fn2;
 import static com.jnape.palatable.lambda.functions.builtin.fn1.Id.id;
 import static com.jnape.palatable.lambda.functions.builtin.fn2.Cons.cons;
+import static com.jnape.palatable.lambda.functions.builtin.fn2.Map.map;
+import static com.jnape.palatable.lambda.lens.Iso.simpleIso;
 import static com.jnape.palatable.lambda.lens.Lens.simpleLens;
+import static com.jnape.palatable.lambda.lens.functions.View.view;
 
 /**
  * Lenses that operate on {@link Iterable}s.
@@ -43,4 +47,16 @@ public static <A> Lens.Simple<Iterable<A>, Maybe<A>> head() {
     public static <A> Lens.Simple<Iterable<A>, Iterable<A>> tail() {
         return simpleLens(Tail::tail, fn2(Head.<A>head().andThen(o -> o.fmap(cons()).orElse(id()))).toBiFunction());
     }
+
+    /**
+     * An iso focusing on the mapped values of an {@link Iterable}.
+     *
+     * @param abIso the iso from A to B
+     * @param <A>   the unmapped {@link Iterable} element type
+     * @param <B>   the mapped {@link Iterable} element type
+     * @return an iso that maps {@link Iterable}&lt;A&gt; to {@link Iterable}&lt;B&gt;
+     */
+    public static <A, B> Iso.Simple<Iterable<A>, Iterable<B>> mapping(Iso<A, A, B, B> abIso) {
+        return simpleIso(map(view(abIso)), map(view(abIso.mirror())));
+    }
 }
diff --git a/src/test/java/com/jnape/palatable/lambda/lens/lenses/IterableLensTest.java b/src/test/java/com/jnape/palatable/lambda/lens/lenses/IterableLensTest.java
@@ -1,12 +1,14 @@
 package com.jnape.palatable.lambda.lens.lenses;
 
 import com.jnape.palatable.lambda.adt.Maybe;
+import com.jnape.palatable.lambda.lens.Iso;
 import com.jnape.palatable.lambda.lens.Lens;
 import org.junit.Test;
 
 import static com.jnape.palatable.lambda.adt.Maybe.just;
 import static com.jnape.palatable.lambda.adt.Maybe.nothing;
 import static com.jnape.palatable.lambda.functions.builtin.fn2.Map.map;
+import static com.jnape.palatable.lambda.lens.Iso.simpleIso;
 import static com.jnape.palatable.lambda.lens.functions.Over.over;
 import static com.jnape.palatable.lambda.lens.functions.Set.set;
 import static com.jnape.palatable.lambda.lens.functions.View.view;
@@ -51,4 +53,19 @@ public void tail() {
         assertThat(over(tail, map(x -> x + 1), emptyList()), isEmpty());
         assertThat(over(tail, map(x -> x + 1), asList(1, 2, 3)), iterates(1, 3, 4));
     }
+
+    @Test
+    public void mapping() {
+        Iso.Simple<Iterable<String>, Iterable<Integer>> iso = IterableLens.mapping(simpleIso(Integer::parseInt, Object::toString));
+
+        assertThat(view(iso, emptyList()), isEmpty());
+        assertThat(view(iso, singletonList("1")), iterates(1));
+        assertThat(view(iso, asList("1", "2", "3")), iterates(1, 2, 3));
+
+        assertThat(set(iso, emptyList(), emptyList()), isEmpty());
+        assertThat(set(iso, singletonList(1), emptyList()), iterates("1"));
+        assertThat(set(iso, singletonList(2), singletonList("1")), iterates("2"));
+        assertThat(set(iso, asList(1, 2, 3), singletonList("1")), iterates("1", "2", "3"));
+        assertThat(set(iso, emptyList(), singletonList("1")), isEmpty());
+    }
 }
