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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
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6 /**
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7 * The Reader monad (also called the function monad, so equivalent to the idea of F).
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8 * Created by MarkPerry on 7/07/2014.
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9 */
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10 public class Reader<A, B> {
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11
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12 private F<A, B> function;
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13
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14 public Reader(F<A, B> f) {
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15 function = f;
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16 }
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17
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18 public F<A, B> getFunction() {
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19 return function;
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20 }
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21
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22 public static <A, B> Reader<A, B> unit(F<A, B> f) {
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23 return new Reader<A, B>(f);
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24 }
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25
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26 public static <A, B> Reader<A, B> constant(B b) {
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27 return unit(a -> b);
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28 }
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29
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30 public B f(A a) {
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31 return function.f(a);
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32 }
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33
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34 public <C> Reader<A, C> map(F<B, C> f) {
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35 return unit(F1Functions.andThen(function, f));
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36 }
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37
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38 public <C> Reader<A, C> andThen(F<B, C> f) {
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39 return map(f);
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40 }
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41
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42 public <C> Reader<A, C> flatMap(F<B, Reader<A, C>> f) {
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43 return unit(a -> f.f(function.f(a)).f(a));
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44 }
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45
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46 public <C> Reader<A, C> bind(F<B, Reader<A, C>> f) {
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47 return flatMap(f);
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48 }
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49
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50 }
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