Change shrinking a bit, add more generators, fix some types, moved suchThat

Shrinking is now done using a "ShrinkStrategy". It's pretty similar to what it
used to be in the end, but instead of generating new ShrinkTree<T>s yourself,
you just generate smaller <T>s, and the generator framework will re-call your
strategy to shrink smaller elements. (So, essentially, ShrinkStrategy.shrink(T
obj) returns an Iterator<T> which then has smaller trees calculated from it.)

Added some more generators. In particular: longs and doubles.

Fixed some types, so now Generator.tuple(integer(), string()) will work. Yay!

Move suchThat to Generator, so now integer().suchThat(x -> x < 10) will work
instead of the old Generators.suchThat(x -> x < 10, integer()), which felt a
bit weird.

1 files changed, 113 insertions, 34 deletions

diff --git a/src/main/java/au/id/zancanaro/javacheck/Generators.java b/src/main/java/au/id/zancanaro/javacheck/Generators.java
index 5dee924..e5699ac 100644
--- a/src/main/java/au/id/zancanaro/javacheck/Generators.java
+++ b/src/main/java/au/id/zancanaro/javacheck/Generators.java
@@ -1,41 +1,40 @@
 package au.id.zancanaro.javacheck;
 
-import java.util.Arrays;
-import java.util.Collections;
-import java.util.Iterator;
-import java.util.List;
+import java.util.*;
 import java.util.function.Function;
-import java.util.function.Predicate;
 
-@SuppressWarnings("unused")
+@SuppressWarnings({"unused", "WeakerAccess"})
 public final class Generators {
     private Generators() {
     }
 
+    /**
+     * Create a generator which explicitly depends on the current "size"
+     * parameter.
+     *
+     * @param makeGenerator A function from size to a generator
+     * @param <T>           The static type of the returned generator
+     * @return The generator returned by makeGenerator
+     */
     public static <T> Generator<T> sized(Function<Integer, Generator<T>> makeGenerator) {
         return (random, size) -> makeGenerator.apply(size).generate(random, size);
     }
 
-    public static <T> Generator<T> suchThat(Generator<T> gen, Predicate<T> predicate) {
-        return (random, size) -> {
-            ShrinkTree<T> result = gen.generate(random, size);
-            if (predicate.test(result.getValue())) {
-                return result.filter(predicate);
-            } else {
-                return suchThat(gen, predicate).generate(random, size);
-            }
-        };
-    }
-
+    /**
+     * Remove a generator's shrink tree.
+     *
+     * @param gen The generator
+     * @param <T> The generator's static type
+     * @return A new generator which is the previous generator with shrink tree
+     * removed
+     */
     public static <T> Generator<T> noShrink(Generator<T> gen) {
-        return (random, size) -> new ShrinkTree<>(
-                gen.generate(random, size).getValue(),
-                Collections.emptyList());
+        return (random, size) -> ShrinkTree.pure(gen.generate(random, size).getValue());
     }
 
     @SafeVarargs
-    public static <T> Generator<T> oneOf(Generator<T>... gens) {
-        return integer(0, gens.length).flatMap(index -> gens[index]);
+    public static <T> Generator<T> oneOf(Generator<? extends T>... gens) {
+        return integer(0, gens.length).flatMap(index -> gens[index].map(x -> (T) x));
     }
 
     public static <T> Generator<T> elements(T[] elements) {
@@ -48,16 +47,67 @@ public final class Generators {
 
     public static Generator<Boolean> bool() {
         return (random, size) ->
-                random.nextBoolean() ?
-                        new ShrinkTree<>(true, Collections.singletonList(new ShrinkTree<>(false, Collections.emptyList()))) :
-                        new ShrinkTree<>(false, Collections.emptyList());
+                ShrinkTree.pure(random.nextBoolean())
+                        .withShrinkStrategy(boolShrinkStrategy());
+    }
+
+    private static ShrinkStrategy<Boolean> boolShrinkStrategy() {
+        return value -> new Iterator<Boolean>() {
+            boolean hasMore = value;
+
+            @Override
+            public boolean hasNext() {
+                return hasMore;
+            }
+
+            @Override
+            public Boolean next() {
+                if (hasMore) {
+                    return (hasMore = false);
+                } else {
+                    throw new NoSuchElementException("Boolean shrink tree exhausted");
+                }
+            }
+        };
+    }
+
+    public static Generator<Long> longInteger(long lower, long upper) {
+        return (random, size) -> {
+            long value = random.longs(lower, upper).findFirst().getAsLong();
+            long bound = lower > 0 ? lower : (upper < 0 ? upper : 0);
+            return ShrinkTree.pure(value)
+                    .withShrinkStrategy(longShrinkStrategy(bound));
+        };
+    }
+
+    public static Generator<Long> longInteger() {
+        return sized(size -> longInteger(-size, size));
+    }
+
+    private static ShrinkStrategy<Long> longShrinkStrategy(final long bound) {
+        return value -> new Iterator<Long>() {
+            long curr = value - bound;
+
+            @Override
+            public boolean hasNext() {
+                return curr != 0;
+            }
+
+            @Override
+            public Long next() {
+                long prevCurr = curr;
+                curr = curr / 2;
+                return value - prevCurr;
+            }
+        };
     }
 
     public static Generator<Integer> integer(int lower, int upper) {
         return (random, size) -> {
-            int value = lower + random.nextInt(upper - lower);
+            int value = random.ints(lower, upper).findFirst().getAsInt();
             int bound = lower > 0 ? lower : (upper < 0 ? upper : 0);
-            return new ShrinkTree<>(value, intShrinkingIterable(value, bound));
+            return ShrinkTree.pure(value)
+                    .withShrinkStrategy(intShrinkStrategy(bound));
         };
     }
 
@@ -69,8 +119,8 @@ public final class Generators {
         return sized(size -> integer(0, size));
     }
 
-    private static Iterable<ShrinkTree<Integer>> intShrinkingIterable(final int value, final int bound) {
-        return () -> new Iterator<ShrinkTree<Integer>>() {
+    public static ShrinkStrategy<Integer> intShrinkStrategy(int bound) {
+        return value -> new Iterator<Integer>() {
             int curr = value - bound;
 
             @Override
@@ -79,10 +129,41 @@ public final class Generators {
             }
 
             @Override
-            public ShrinkTree<Integer> next() {
+            public Integer next() {
                 int prevCurr = curr;
                 curr = curr / 2;
-                return new ShrinkTree<>(value - prevCurr, intShrinkingIterable(value - prevCurr, bound));
+                return value - prevCurr;
+            }
+        };
+    }
+
+    public static Generator<Double> doublePrecision(double lower, double upper) {
+        return (random, size) -> {
+            double value = random.doubles(lower, upper).findFirst().getAsDouble();
+            double bound = lower > 0 ? lower : (upper < 0 ? upper : 0);
+            return ShrinkTree.pure(value)
+                    .withShrinkStrategy(doubleShrinkStrategy(bound, Double.MIN_NORMAL /* maybe pick a bigger epsilon? */));
+        };
+    }
+
+    public static Generator<Double> doublePrecision() {
+        return sized(size -> doublePrecision(-size, size));
+    }
+
+    public static ShrinkStrategy<Double> doubleShrinkStrategy(double bound, double epsilon) {
+        return value -> new Iterator<Double>() {
+            double curr = value - bound;
+
+            @Override
+            public boolean hasNext() {
+                return Math.abs(curr) > epsilon;
+            }
+
+            @Override
+            public Double next() {
+                double prevCurr = curr;
+                curr = curr / 2;
+                return value - prevCurr;
             }
         };
     }
@@ -93,9 +174,7 @@ public final class Generators {
             int count = countGen.generate(random, size).getValue();
             return Generator.list(count, gen)
                     .generate(random, size)
-                    .filter(list ->
-                            minElements <= list.size()
-                                    && list.size() < maxElements)
+                    .filter(list -> minElements <= list.size() && list.size() < maxElements)
                     .map(Collections::unmodifiableList);
         };
     }