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mperrymperry
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Added tests to the reader monad
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Lines changed: 107 additions & 4 deletions

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‎core/src/main/java/fj/data/Reader.java‎

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import fj.F1Functions;
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/**
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* The Reader monad (also called the function monad, so equivalent to the idea of F).
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* Created by MarkPerry on 7/07/2014.
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*/
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public class Reader<A, B> {

‎core/src/test/java/fj/data/ReaderTest.java‎

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package fj.data;
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import fj.data.Reader;
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import org.junit.Assert;
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import fj.F;
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import fj.F2;
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import fj.test.*;
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import org.junit.Test;
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import static fj.F1Functions.bind;
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import static fj.F1Functions.map;
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import static fj.F2Functions.curry;
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import static fj.test.Arbitrary.arbF;
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import static fj.test.Arbitrary.arbF2;
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import static fj.test.Arbitrary.arbInteger;
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import static fj.test.Coarbitrary.coarbInteger;
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import static fj.test.Property.prop;
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import static fj.test.Property.property;
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import static org.junit.Assert.assertTrue;
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/**
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* Created by MarkPerry on 4/12/2014.
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*
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* Examples taken from http://learnyouahaskell.com/for-a-few-monads-more
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*/
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public class ReaderTest {
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@Test
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public void testMap() {
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// (3 + 8) * 11
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// example taken from http://learnyouahaskell.com/for-a-few-monads-more
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int x = Reader.unit((Integer i) -> i + 3).map(i -> i * 5).f(8);
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assertTrue(x == 55);
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// System.out.println(x); // 55
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}
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@Test
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public void testFlatMap() {
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// (3 * 2) + (3 + 10)
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// example taken from http://learnyouahaskell.com/for-a-few-monads-more
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int y = Reader.unit((Integer i) -> i * 2).flatMap(a -> Reader.unit((Integer i) -> i + 10).map(b -> a + b)).f(3);
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// System.out.println(y); // 19
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assertTrue(y == 19);
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}
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@Test
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public void testMapProp() {
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CheckResult cr = property(
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arbF(coarbInteger, arbInteger),
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arbF(coarbInteger, arbInteger),
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arbInteger,
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(f, g, i) -> {
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int expected = map(f, g).f(i);
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// System.out.println(String.format("input: %d, result: %d", i, expected));
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return prop(expected == Reader.unit(f).map(g).f(i));
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}).check();
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CheckResult.summary.println(cr);
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assertTrue(cr.isExhausted() || cr.isPassed() || cr.isProven());
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}
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@Test
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public void testFlatMapProp() {
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CheckResult cr = property(
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arbF(coarbInteger, arbInteger),
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arbF2(coarbInteger, coarbInteger, arbInteger),
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arbInteger,
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(f, g, i) -> {
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int expected = bind(f, curry(g)).f(i);
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// System.out.println(String.format("input: %d, result: %d", i, expected));
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return prop(expected == Reader.unit(f).flatMap(toBindable(g)).f(i));
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}
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).check();
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CheckResult.summary.println(cr);
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assertTrue(cr.isExhausted() || cr.isPassed() || cr.isProven());
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}
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@Test
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public void testLeftIdentity() {
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CheckResult cr = Property.property(
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arbInteger,
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arbF(coarbInteger, arbInteger),
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arbF2(coarbInteger, coarbInteger, arbInteger),
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(i, f, g) -> {
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// F<Integer, Reader<Integer, Integer>> h = convert(g);
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int a = Reader.unit(f).flatMap(toBindable(g)).f(i);
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int b = g.f(f.f(i), i);
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// System.out.println(String.format("i=%d, a=%d, b=%d, truth=%b", i, a, b, a == b));
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return prop(a == b);
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}).check();
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CheckResult.summary.println(cr);
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assertTrue(cr.isExhausted() || cr.isPassed() || cr.isProven());
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}
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F<Integer, Reader<Integer, Integer>> toBindable(F2<Integer, Integer, Integer> f) {
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// F<Integer, Reader<Integer, Integer>> h = map(curry(f), z -> Reader.unit(z));
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return map(curry(f), z -> Reader.unit(z));
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}
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@Test
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public void testRightIdentity() {
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CheckResult cr = Property.property(
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arbInteger,
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arbF(coarbInteger, arbInteger),
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(i, f) -> {
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Reader<Integer, Integer> r = Reader.unit(f);
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boolean b = r.flatMap(a -> r).f(i) == r.f(i);
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// System.out.println(String.format("i=%d, a=%d, b=%d, truth=%b", i, a, b, a == b));
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return prop(b);
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}).check();
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CheckResult.summary.println(cr);
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assertTrue(cr.isExhausted() || cr.isPassed() || cr.isProven());
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}
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@Test
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public void testAssociativity() {
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CheckResult cr = Property.property(
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arbInteger,
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arbF(coarbInteger, arbInteger),
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arbF2(coarbInteger, coarbInteger, arbInteger),
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arbF2(coarbInteger, coarbInteger, arbInteger),
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(i, f, g, h) -> {
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Reader<Integer, Integer> r = Reader.unit(f);
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int a = r.flatMap(toBindable(g)).flatMap(toBindable(h)).f(i);
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int b = r.flatMap(x -> toBindable(g).f(x).flatMap(toBindable(h))).f(i);
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// System.out.println(String.format("i=%d, a=%d, b=%d, truth=%b", i, a, b, a == b));
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return prop(a == b);
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}).check();
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CheckResult.summary.println(cr);
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assertTrue(cr.isExhausted() || cr.isPassed() || cr.isProven());
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}
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}

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