IO internal rewrite

- now sealed
- linear and recursive composition is stack-safe
- static factory methods are now much easier to infer

Author: jnape

CHANGELOG.md

@@ -4,7 +4,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/).
 
 ## [Unreleased]
-No changes
+### Changed
+- ***Breaking Change***: `IO` is now sealed. Most previous constructions using the static factory methods
+should continue to work (by simply targeting `Supplier` now instead of an anonymous `IO`), but some might
+need to be reworked, and subtyping is obviously no longer supported.
+- `IO` is now stack-safe, regardless of whether the composition nests linearly or recursively
 
 ## [3.3.0] - 2019-02-18
 ### Added

src/main/java/com/jnape/palatable/lambda/functions/Effect.java

@@ -6,7 +6,6 @@
 import java.util.function.Consumer;
 import java.util.function.Function;
 
-import static com.jnape.palatable.lambda.functions.Fn0.fn0;
 import static com.jnape.palatable.lambda.functions.IO.io;
 import static com.jnape.palatable.lambda.functions.builtin.fn1.Constantly.constantly;
 
@@ -22,7 +21,7 @@ public interface Effect<A> extends Fn1<A, IO<Unit>>, Consumer<A> {
 
     @Override
     default IO<Unit> apply(A a) {
-        return io(fn0(() -> accept(a)));
+        return io(() -> accept(a));
     }
 
     @Override

src/main/java/com/jnape/palatable/lambda/functions/Fn0.java

@@ -9,7 +9,6 @@
 import java.util.function.Supplier;
 
 import static com.jnape.palatable.lambda.adt.Unit.UNIT;
-import static com.jnape.palatable.lambda.functions.IO.io;
 
 /**
  * A function taking "no arguments", implemented as an <code>{@link Fn1}&lt;{@link Unit}, A&gt;</code>.
@@ -124,7 +123,10 @@ static <A> Fn0<A> fn0(Fn0<A> fn) {
      * @return the {@link Fn0}
      */
     static Fn0<Unit> fn0(Runnable runnable) {
-        return io(runnable)::unsafePerformIO;
+        return fn0(() -> {
+            runnable.run();
+            return UNIT;
+        });
     }
 
     /**