Filter automatically deforests

jnape · jnape · commit e1c9275e497d · 2018-02-24T17:21:18.000-06:00
diff --git a/src/main/java/com/jnape/palatable/lambda/functions/builtin/fn2/Filter.java b/src/main/java/com/jnape/palatable/lambda/functions/builtin/fn2/Filter.java
@@ -2,7 +2,7 @@
 
 import com.jnape.palatable.lambda.functions.Fn1;
 import com.jnape.palatable.lambda.functions.Fn2;
-import com.jnape.palatable.lambda.iteration.FilteringIterator;
+import com.jnape.palatable.lambda.iteration.FilteringIterable;
 
 import java.util.function.Function;
 
@@ -23,7 +23,7 @@ private Filter() {
 
     @Override
     public Iterable<A> apply(Function<? super A, Boolean> predicate, Iterable<A> as) {
-        return () -> new FilteringIterator<>(predicate, as.iterator());
+        return new FilteringIterable<>(predicate, as);
     }
 
     @SuppressWarnings("unchecked")
diff --git a/src/main/java/com/jnape/palatable/lambda/iteration/FilteringIterable.java b/src/main/java/com/jnape/palatable/lambda/iteration/FilteringIterable.java
@@ -0,0 +1,31 @@
+package com.jnape.palatable.lambda.iteration;
+
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+import java.util.function.Function;
+
+import static com.jnape.palatable.lambda.functions.builtin.fn2.All.all;
+import static java.util.Collections.singletonList;
+
+public final class FilteringIterable<A> implements Iterable<A> {
+    private final List<Function<? super A, Boolean>> predicates;
+    private final Iterable<A>                        as;
+
+    public FilteringIterable(Function<? super A, Boolean> predicate, Iterable<A> as) {
+        List<Function<? super A, Boolean>> predicates = new ArrayList<>(singletonList(predicate));
+        while (as instanceof FilteringIterable) {
+            FilteringIterable<A> nested = (FilteringIterable<A>) as;
+            predicates.addAll(nested.predicates);
+            as = nested.as;
+        }
+        this.predicates = predicates;
+        this.as = as;
+    }
+
+    @Override
+    public Iterator<A> iterator() {
+        Function<? super A, Boolean> metaPredicate = a -> all(p -> p.apply(a), predicates);
+        return new FilteringIterator<>(metaPredicate, as.iterator());
+    }
+}
diff --git a/src/test/java/com/jnape/palatable/lambda/iteration/FilteringIterableTest.java b/src/test/java/com/jnape/palatable/lambda/iteration/FilteringIterableTest.java
@@ -0,0 +1,19 @@
+package com.jnape.palatable.lambda.iteration;
+
+import com.jnape.palatable.lambda.functions.Fn1;
+import com.jnape.palatable.traitor.annotations.TestTraits;
+import com.jnape.palatable.traitor.runners.Traits;
+import org.junit.runner.RunWith;
+import testsupport.traits.Deforesting;
+
+import static com.jnape.palatable.lambda.functions.builtin.fn1.Constantly.constantly;
+import static com.jnape.palatable.lambda.functions.builtin.fn2.Filter.filter;
+
+@RunWith(Traits.class)
+public class FilteringIterableTest {
+
+    @TestTraits({Deforesting.class})
+    public Fn1<Iterable<Integer>, Iterable<Integer>> testSubject() {
+        return filter(constantly(true));
+    }
+}
