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1 package fj.test;
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2
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3 import fj.F;
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4 import fj.data.Option;
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5 import static fj.data.Option.some;
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6
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7 import static java.lang.Math.max;
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8 import static java.lang.Math.min;
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9 import java.util.Random;
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10
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11 /**
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12 * A random number generator.
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13 *
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14 * @version %build.number%
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15 */
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16 public final class Rand {
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17 private final F<Option<Long>, F<Integer, F<Integer, Integer>>> f;
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18 private final F<Option<Long>, F<Double, F<Double, Double>>> g;
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19
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20 private Rand(final F<Option<Long>, F<Integer, F<Integer, Integer>>> f, final F<Option<Long>, F<Double, F<Double, Double>>> g) {
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21 this.f = f;
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22 this.g = g;
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23 }
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24
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25 /**
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26 * Randomly chooses a value between the given range (inclusive).
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27 *
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28 * @param seed The seed to use for random generation.
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29 * @param from The minimum value to choose.
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30 * @param to The maximum value to choose.
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31 * @return A random value in the given range.
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32 */
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33 public int choose(final long seed, final int from, final int to) {
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34 return f.f(some(seed)).f(from).f(to);
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35 }
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36
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37 /**
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38 * Randomly chooses a value between the given range (inclusive).
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39 *
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40 * @param from The minimum value to choose.
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41 * @param to The maximum value to choose.
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42 * @return A random value in the given range.
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43 */
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44 public int choose(final int from, final int to) {
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45 return f.f(Option.<Long>none()).f(from).f(to);
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46 }
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47
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48 /**
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49 * Randomly chooses a value between the given range (inclusive).
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50 *
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51 * @param seed The seed to use for random generation.
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52 * @param from The minimum value to choose.
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53 * @param to The maximum value to choose.
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54 * @return A random value in the given range.
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55 */
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56 public double choose(final long seed, final double from, final double to) {
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57 return g.f(some(seed)).f(from).f(to);
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58 }
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59
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60 /**
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61 * Randomly chooses a value between the given range (inclusive).
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62 *
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63 * @param from The minimum value to choose.
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64 * @param to The maximum value to choose.
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65 * @return A random value in the given range.
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66 */
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67 public double choose(final double from, final double to) {
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68 return g.f(Option.<Long>none()).f(from).f(to);
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69 }
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70
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71 /**
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72 * Gives this random generator a new seed.
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73 *
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74 * @param seed The seed of the new random generator.
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75 * @return A random generator with the given seed.
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76 */
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77 public Rand reseed(final long seed) {
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78 return new Rand(new F<Option<Long>, F<Integer, F<Integer, Integer>>>() {
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79 public F<Integer, F<Integer, Integer>> f(final Option<Long> old) {
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80 return new F<Integer, F<Integer, Integer>>() {
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81 public F<Integer, Integer> f(final Integer from) {
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82 return new F<Integer, Integer>() {
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83 public Integer f(final Integer to) {
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84 return f.f(some(seed)).f(from).f(to);
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85 }
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86 };
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87 }
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88 };
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89 }
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90 }, new F<Option<Long>, F<Double, F<Double, Double>>>() {
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91 public F<Double, F<Double, Double>> f(final Option<Long> old) {
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92 return new F<Double, F<Double, Double>>() {
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93 public F<Double, Double> f(final Double from) {
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94 return new F<Double, Double>() {
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95 public Double f(final Double to) {
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96 return g.f(some(seed)).f(from).f(to);
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97 }
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98 };
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99 }
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100 };
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101 }
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102 });
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103 }
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104
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105 /**
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106 * Constructs a random generator from the given functions that supply a range to produce a
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107 * result.
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108 *
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109 * @param f The integer random generator.
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110 * @param g The floating-point random generator.
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111 * @return A random generator from the given functions that supply a range to produce a result.
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112 */
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113 public static Rand rand(final F<Option<Long>, F<Integer, F<Integer, Integer>>> f, final F<Option<Long>, F<Double, F<Double, Double>>> g) {
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114 return new Rand(f, g);
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115 }
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116
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117
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118 private static final F<Long, Random> fr = new F<Long, Random>() {
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119 public Random f(final Long x) {
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120 return new Random(x);
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121 }
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122 };
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123
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124 /**
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125 * A standard random generator that uses {@link Random}.
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126 */
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127 public static final Rand standard = new Rand(new F<Option<Long>, F<Integer, F<Integer, Integer>>>() {
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128 public F<Integer, F<Integer, Integer>> f(final Option<Long> seed) {
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129 return new F<Integer, F<Integer, Integer>>() {
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130 public F<Integer, Integer> f(final Integer from) {
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131 return new F<Integer, Integer>() {
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132 public Integer f(final Integer to) {
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133 final int f = min(from, to);
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134 final int t = max(from, to);
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135 return f + seed.map(fr).orSome(new Random()).nextInt(t - f + 1);
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136 }
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137 };
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138 }
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139 };
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140 }
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141 }, new F<Option<Long>, F<Double, F<Double, Double>>>() {
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142 public F<Double, F<Double, Double>> f(final Option<Long> seed) {
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143 return new F<Double, F<Double, Double>>() {
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144 public F<Double, Double> f(final Double from) {
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145 return new F<Double, Double>() {
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146 public Double f(final Double to) {
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147 final double f = min(from, to);
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148 final double t = max(from, to);
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149 return seed.map(fr).orSome(new Random()).nextDouble() * (t - f) + f;
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150 }
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151 };
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152 }
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153 };
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154 }
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155 });
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156 }
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