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1 package fj.data;
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2
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3 import fj.F;
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4 import fj.data.test.PropertyAssert;
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5 import fj.test.*;
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6 import org.junit.Test;
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7
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8 import static fj.F1Functions.bind;
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9 import static fj.F1Functions.map;
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10 import static fj.test.Arbitrary.*;
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11 import static fj.test.Coarbitrary.coarbInteger;
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12 import static fj.test.Property.prop;
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13 import static fj.test.Property.property;
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14 import static org.junit.Assert.assertTrue;
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15
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16 /**
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17 * Created by MarkPerry on 4/12/2014.
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18 */
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19 public class ReaderTest {
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20
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21 @Test
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22 public void testMap() {
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23 // (3 + 8) * 11
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24 // example taken from http://learnyouahaskell.com/for-a-few-monads-more
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25 int x = Reader.unit((Integer i) -> i + 3).map(i -> i * 5).f(8);
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26 assertTrue(x == 55);
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27 // System.out.println(x); // 55
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28 }
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29
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30 @Test
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31 public void testFlatMap() {
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32 // (3 * 2) + (3 + 10)
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33 // example taken from http://learnyouahaskell.com/for-a-few-monads-more
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34 int y = (int) Reader.unit((Integer i) -> i * 2).flatMap(a -> Reader.unit((Integer i) -> i + 10).map(b -> a + b)).f(3);
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35 // System.out.println(y); // 19
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36 assertTrue(y == 19);
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37 }
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38
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39 @Test
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40 public void testMapProp() {
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41 Property p = property(
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42 arbF(coarbInteger, arbInteger),
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43 arbF(coarbInteger, arbInteger),
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44 arbInteger,
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45 (f, g, i) -> {
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46 int expected = map(f, g).f(i);
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47 // System.out.println(String.format("input: %d, result: %d", i, expected));
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48 return prop(expected == Reader.unit(f).map(g).f(i));
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49 });
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50 PropertyAssert.assertResult(p);
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51 }
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52
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53 @Test
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54 public void testFlatMapProp() {
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55 Arbitrary<F<Integer, Reader<Integer, Integer>>> a = arbF(coarbInteger, arbReader());
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56 Property p = property(
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57 arbF(coarbInteger, arbInteger),
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58 a,
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59 arbInteger,
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60 (f, g, i) -> {
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61 int expected = bind(f, j -> g.f(j).getFunction()).f(i);
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62 // System.out.println(String.format("input: %d, result: %d", i, expected));
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63 return prop(expected == Reader.unit(f).flatMap(g).f(i));
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64 }
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65 );
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66 PropertyAssert.assertResult(p);
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67 }
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68
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69 // Left identity: return a >>= f == f a
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70 @Test
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71 public void testLeftIdentity() {
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72 Property p = Property.property(
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73 arbInteger,
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74 arbInteger,
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75 arbF(coarbInteger, arbReader()),
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76 (i, j, f) -> {
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77 int a = Reader.<Integer, Integer>constant(i).flatMap(f).f(j);
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78 int b = f.f(i).f(j);
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79 return prop(a == b);
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80 });
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81 PropertyAssert.assertResult(p);
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82 }
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83
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84 // Right identity: m >>= return == m
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85 @Test
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86 public void testRightIdentity() {
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87 Property p = Property.property(
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88 arbInteger,
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89 arbReader(),
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90 (i, r2) -> {
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91 return prop(r2.flatMap(a -> Reader.constant(a)).f(i) == r2.f(i));
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92 });
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93 PropertyAssert.assertResult(p);
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94 }
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95
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96 // Associativity: (m >>= f) >>= g == m >>= (\x -> f x >>= g)
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97 @Test
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98 public void testAssociativity() {
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99 Property p = Property.property(
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100 arbInteger,
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101 arbReader(),
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102 arbF(coarbInteger, arbReader()),
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103 arbF(coarbInteger, arbReader()),
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104 (i, r, f, g) -> {
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105 boolean b2 = r.flatMap(f).flatMap(g).f(i) == r.flatMap(x -> f.f(x).flatMap(g)).f(i);
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106 return prop(b2);
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107 });
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108 PropertyAssert.assertResult(p);
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109 }
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110
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111 public Arbitrary<Reader<Integer, Integer>> arbReader() {
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112 return Arbitrary.arbReader(coarbInteger, arbInteger);
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113 }
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114
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115
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116 }
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