#all: returns true if all members of an Iterable succeed for a predicate evaluation; false otherwise

jnape · jnape · commit b8b3105befbf · 2014-03-11T15:48:47.000-07:00
diff --git a/src/main/java/com/jnape/palatable/lambda/functions/All.java b/src/main/java/com/jnape/palatable/lambda/functions/All.java
@@ -0,0 +1,28 @@
+package com.jnape.palatable.lambda.functions;
+
+import com.jnape.palatable.lambda.DyadicFunction;
+import com.jnape.palatable.lambda.MonadicFunction;
+
+public final class All<A> extends DyadicFunction<MonadicFunction<? super A, Boolean>, Iterable<A>, Boolean> {
+
+    @Override
+    public final Boolean apply(MonadicFunction<? super A, Boolean> predicate, Iterable<A> as) {
+        for (A a : as)
+            if (!predicate.apply(a))
+                return false;
+
+        return true;
+    }
+
+    public static <A> All<A> all() {
+        return new All<A>();
+    }
+
+    public static <A> MonadicFunction<Iterable<A>, Boolean> all(MonadicFunction<? super A, Boolean> predicate) {
+        return All.<A>all().partial(predicate);
+    }
+
+    public static <A> boolean all(MonadicFunction<? super A, Boolean> predicate, Iterable<A> as) {
+        return all(predicate).apply(as);
+    }
+}
diff --git a/src/test/java/com/jnape/palatable/lambda/functions/AllTest.java b/src/test/java/com/jnape/palatable/lambda/functions/AllTest.java
@@ -0,0 +1,49 @@
+package com.jnape.palatable.lambda.functions;
+
+import com.jnape.palatable.lambda.MonadicFunction;
+import com.jnape.palatable.lambda.Predicate;
+import com.jnape.palatable.traitor.annotations.TestTraits;
+import com.jnape.palatable.traitor.runners.Traits;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import testsupport.traits.EmptyIterableSupport;
+
+import static com.jnape.palatable.lambda.builtin.monadic.Always.always;
+import static com.jnape.palatable.lambda.functions.All.all;
+import static com.jnape.palatable.lambda.functions.Repeat.repeat;
+import static java.util.Arrays.asList;
+import static org.hamcrest.core.Is.is;
+import static org.junit.Assert.assertThat;
+
+@RunWith(Traits.class)
+public class AllTest {
+
+    private static final MonadicFunction<? super Number, Boolean> EVEN = new Predicate<Number>() {
+        @Override
+        public Boolean apply(Number number) {
+            return number.doubleValue() % 2 == 0;
+        }
+    };
+
+    @TestTraits({EmptyIterableSupport.class})
+    public MonadicFunction<Iterable<Object>, Boolean> createTestSubject() {
+        return all(always(true));
+    }
+
+    @Test
+    public void trueIfAllElementsMatchPredicate() {
+        Iterable<Integer> numbers = asList(2, 4, 6, 8);
+        assertThat(all(EVEN, numbers), is(true));
+    }
+
+    @Test
+    public void falseIfAnyElementsFailPredicate() {
+        Iterable<Integer> numbers = asList(1, 2, 4, 6, 8);
+        assertThat(all(EVEN, numbers), is(false));
+    }
+
+    @Test
+    public void terminatesIterationImmediatelyUponPredicateFailure() {
+        assertThat(all(EVEN, repeat(1)), is(false));
+    }
+}
diff --git a/src/test/java/testsupport/traits/EmptyIterableSupport.java b/src/test/java/testsupport/traits/EmptyIterableSupport.java
@@ -5,10 +5,10 @@
 
 import java.util.ArrayList;
 
-public class EmptyIterableSupport implements Trait<MonadicFunction<Iterable, Iterable>> {
+public class EmptyIterableSupport implements Trait<MonadicFunction<Iterable, ?>> {
 
     @Override
-    public void test(MonadicFunction<Iterable, Iterable> testSubject) {
+    public void test(MonadicFunction<Iterable, ?> testSubject) {
         try {
             testSubject.apply(new ArrayList());
         } catch (Exception e) {
