Introduced F0 interface for lazy values equivalent to P1

mperry · mperry · commit 97278b42a24d · 2015-01-22T01:43:00.000+10:00
diff --git a/core/src/main/java/fj/F0.java b/core/src/main/java/fj/F0.java
@@ -0,0 +1,10 @@
+package fj;
+
+/**
+ * Created by MarkPerry on 21/01/2015.
+ */
+public interface F0<A> {
+
+    public A f();
+
+}
diff --git a/core/src/main/java/fj/P.java b/core/src/main/java/fj/P.java
@@ -675,15 +675,19 @@ public H _8() {
     };
   }
 
-    public static <A> P1<A> lazy(F<Unit, A> f) {
+    public static <A> P1<A> lazy(F0<A> f) {
         return new P1<A>() {
             @Override
             public A _1() {
-                return f.f(unit());
+                return f.f();
             }
         };
     }
 
+    public static <A> P1<A> lazy(F<Unit, A> f) {
+        return lazy(() -> f.f(unit()));
+    }
+
     public static <A, B> P2<A, B> lazy(F<Unit, A> fa, F<Unit, B> fb) {
         return new P2<A, B>() {
             @Override
diff --git a/core/src/main/java/fj/P1.java b/core/src/main/java/fj/P1.java
@@ -8,7 +8,12 @@
 import fj.data.Validation;
 import fj.function.Try0;
 
-public abstract class P1<A> {
+public abstract class P1<A> implements F0<A> {
+
+    @Override
+    public A f() {
+        return _1();
+    }
 
     /**
      * Access the first element of the product.
diff --git a/core/src/main/java/fj/control/parallel/Promise.java b/core/src/main/java/fj/control/parallel/Promise.java
@@ -1,12 +1,7 @@
 package fj.control.parallel;
 
-import fj.Effect;
-import fj.F;
-import fj.F2;
-import fj.P;
-import fj.P1;
-import fj.P2;
-import fj.Unit;
+import fj.*;
+
 import static fj.P.p;
 import static fj.Function.curry;
 import static fj.Function.identity;
@@ -353,11 +348,7 @@ public static <A, B> F<Stream<A>, Promise<B>> foldRightS(final Strategy<Unit> s,
     return new F<Stream<A>, Promise<B>>() {
       public Promise<B> f(final Stream<A> as) {
         return as.isEmpty() ? promise(s, P.p(b)) : liftM2(f).f(promise(s, P.p(as.head()))).f(
-            Promise.<P1<B>>join(s, new P1<Promise<P1<B>>>() {
-              public Promise<P1<B>> _1() {
-                return f(as.tail()._1()).fmap(P.<B>p1());
-              }
-            }));
+                Promise.<P1<B>>join(s, P.lazy(u -> f(as.tail()._1()).fmap(P.<B>p1()))));
       }
     };
   }
diff --git a/demo/src/main/java/fj/demo/concurrent/MapReduce.java b/demo/src/main/java/fj/demo/concurrent/MapReduce.java
@@ -1,9 +1,6 @@
 package fj.demo.concurrent;
 
-import fj.F;
-import fj.F1Functions;
-import fj.P1;
-import fj.Unit;
+import fj.*;
 import fj.control.parallel.ParModule;
 import static fj.control.parallel.ParModule.parModule;
 import fj.control.parallel.Promise;
@@ -58,11 +55,7 @@ public Stream<Character> f(final BufferedReader reader) {
                     throw new Error(e);
                 }
                 if (s.isSome())
-                    return fromString(s.some()).append(new P1<Stream<Character>>() {
-                        public Stream<Character> _1() {
-                            return f(reader);
-                        }
-                    });
+                    return fromString(s.some()).append(P.lazy(sc -> f(reader)));
                 else {
                     try {
                         reader.close();
