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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.F1Functions;
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5 import fj.function.Effect1;
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6
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7 import static fj.data.Option.some;
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8 import static fj.data.Option.somes;
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9
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10 import java.util.Collection;
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11 import java.util.Iterator;
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12
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13 /**
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14 * Provides an in-memory, immutable, singly linked list with total <code>head</code> and <code>tail</code>.
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15 *
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16 * @version %build.number%
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17 */
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18 public final class NonEmptyList<A> implements Iterable<A> {
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19 /**
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20 * Returns an iterator for this non-empty list. This method exists to permit the use in a <code>for</code>-each loop.
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21 *
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22 * @return A iterator for this non-empty list.
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23 */
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24
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25 public Iterator<A> iterator() {
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26 return toCollection().iterator();
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27 }
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28
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29 /**
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30 * The first element of this linked list.
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31 */
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32 @SuppressWarnings({"PublicField", "ClassEscapesDefinedScope"})
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33 public final A head;
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34
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35 /**
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36 * This list without the first element.
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37 */
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38 @SuppressWarnings({"PublicField"})
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39 public final List<A> tail;
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40
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41 private NonEmptyList(final A head, final List<A> tail) {
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42 this.head = head;
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43 this.tail = tail;
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44 }
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45
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46 /**
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47 * Prepend the given value to this list.
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48 *
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49 * @param a The value to prepend.
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50 * @return A non-empty list with an extra element.
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51 */
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52 public NonEmptyList<A> cons(final A a) {
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53 return nel(a, tail.cons(head));
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54 }
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55
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56 /**
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57 * Appends the given list to this list.
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58 *
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59 * @param as The list to append.
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60 * @return A new list with the given list appended.
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61 */
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62 public NonEmptyList<A> append(final NonEmptyList<A> as) {
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63 final List.Buffer<A> b = new List.Buffer<A>();
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64 b.append(tail);
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65 b.snoc(as.head);
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66 b.append(as.tail);
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67 final List<A> bb = b.toList();
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68 return nel(head, bb);
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69 }
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70
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71 /**
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72 * Maps the given function across this list.
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73 *
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74 * @param f The function to map across this list.
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75 * @return A new list after the given function has been applied to each element.
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76 */
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77 public <B> NonEmptyList<B> map(final F<A, B> f) {
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78 return nel(f.f(head), tail.map(f));
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79 }
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80
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81 /**
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82 * Binds the given function across each element of this list with a final join.
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83 *
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84 * @param f The function to apply to each element of this list.
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85 * @return A new list after performing the map, then final join.
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86 */
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87 public <B> NonEmptyList<B> bind(final F<A, NonEmptyList<B>> f) {
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88 final List.Buffer<B> b = new List.Buffer<B>();
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89 final NonEmptyList<B> p = f.f(head);
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90 b.snoc(p.head);
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91 b.append(p.tail);
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92 tail.foreachDoEffect(new Effect1<A>() {
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93 public void f(final A a) {
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94 final NonEmptyList<B> p = f.f(a);
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95 b.snoc(p.head);
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96 b.append(p.tail);
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97 }
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98 });
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99 final List<B> bb = b.toList();
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100 return nel(bb.head(), bb.tail());
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101 }
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102
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103 /**
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104 * Returns a NonEmptyList of the sublists of this list.
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105 *
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106 * @return a NonEmptyList of the sublists of this list.
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107 */
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108 public NonEmptyList<NonEmptyList<A>> sublists() {
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109 return fromList(
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110 somes(toList().toStream().substreams()
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111 .map(F1Functions.o(new F<List<A>, Option<NonEmptyList<A>>>() {
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112 public Option<NonEmptyList<A>> f(final List<A> list) {
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113 return fromList(list);
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114 }
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115 }, Conversions.<A>Stream_List())).toList())).some();
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116 }
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117
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118 /**
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119 * Returns a NonEmptyList of the tails of this list. A list is considered a tail of itself for the purpose of this
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120 * function (Comonad pattern).
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121 *
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122 * @return A NonEmptyList of the tails of this list.
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123 */
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124 public NonEmptyList<NonEmptyList<A>> tails() {
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125 return fromList(somes(toList().tails().map(new F<List<A>, Option<NonEmptyList<A>>>() {
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126 public Option<NonEmptyList<A>> f(final List<A> list) {
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127 return fromList(list);
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128 }
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129 }))).some();
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130 }
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131
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132 /**
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133 * Maps the given function across the tails of this list (comonad pattern).
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134 *
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135 * @param f The function to map across the tails of this list.
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136 * @return The results of applying the given function to the tails of this list, as a NonEmptyList.
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137 */
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138 public <B> NonEmptyList<B> mapTails(final F<NonEmptyList<A>, B> f) {
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139 return tails().map(f);
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140 }
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141
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142 /**
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143 * Returns a <code>List</code> projection of this list.
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144 *
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145 * @return A <code>List</code> projection of this list.
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146 */
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147 public List<A> toList() {
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148 return tail.cons(head);
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149 }
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150
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151 /**
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152 * Projects an immutable collection of this non-empty list.
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153 *
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154 * @return An immutable collection of this non-empty list.
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155 */
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156 public Collection<A> toCollection() {
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157 return toList().toCollection();
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158 }
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159
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160 /**
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161 * Returns a function that takes a non-empty list to a list.
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162 *
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163 * @return A function that takes a non-empty list to a list.
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164 */
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165 public static <A> F<NonEmptyList<A>, List<A>> toList_() {
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166 return new F<NonEmptyList<A>, List<A>>() {
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167 public List<A> f(final NonEmptyList<A> as) {
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168 return as.toList();
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169 }
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170 };
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171 }
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172
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173 /**
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174 * Return a non-empty list with the given head and tail.
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175 *
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176 * @param head The first element of the new list.
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177 * @param tail The remaining elements of the new list.
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178 * @return A non-empty list with the given head and tail.
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179 */
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180 public static <A> NonEmptyList<A> nel(final A head, final List<A> tail) {
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181 return new NonEmptyList<A>(head, tail);
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182 }
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183
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184 /**
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185 * Return a non-empty list with the given value.
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186 *
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187 * @param head The value in the non-empty list.
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188 * @return A non-empty list with the given value.
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189 */
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190 public static <A> NonEmptyList<A> nel(final A head) {
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191 return nel(head, List.<A>nil());
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192 }
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193
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194 /**
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195 * Returns a function that puts an element into a non-empty list.
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196 *
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197 * @return A function that puts an element into a non-empty list.
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198 */
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199 public static <A> F<A, NonEmptyList<A>> nel() {
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200 return new F<A, NonEmptyList<A>>() {
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201 public NonEmptyList<A> f(final A a) {
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202 return nel(a);
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203 }
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204 };
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205 }
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206
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207 /**
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208 * Returns a potential non-empty list from the given list. A non-value is returned if the given list is empty.
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209 *
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210 * @param as The list to construct a potential non-empty list with.
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211 * @return A potential non-empty list from the given list.
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212 */
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213 public static <A> Option<NonEmptyList<A>> fromList(final List<A> as) {
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214 return as.isEmpty() ?
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215 Option.<NonEmptyList<A>>none() :
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216 some(nel(as.head(), as.tail()));
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217 }
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218 }
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