AdaptorFunctors


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2   // $Id: AdaptorFunctors.java,v 1.2 2006/12/16 16:48:58 davidahall Exp $
3   // Copyright (c) 2006  David A. Hall
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32  
33  package net.sf.jga.fn.adaptor;
34  
35  import java.util.Iterator  ;
36  import net.sf.jga.fn.BinaryFunctor;
37  import net.sf.jga.fn.Generator;
38  import net.sf.jga.fn.UnaryFunctor;
39  
40  /**
41   * Static factory methods for selected functors in the Adaptor package.
42   * <p>
43   * Copyright &copy; 2006  David A. Hall
44   * @author <a HREF="mailto:davidahall@users.sf.net">David A. Hall</a>
45   */
46  
47  public final class AdaptorFunctors {
48      
49      // Stateless functors for which only one instance is really necessary
50      static private Identity _id = new Identity();
51      static private Project1st _proj1 = new Project1st();
52      static private Project2nd _proj2 = new Project2nd();
53  
54      /**
55       * Returns a Boolean Generator that produces TRUE when both input generators return TRUE.
56       */
57      static public Generator<Boolean  > and(Generator<Boolean  > g1, Generator<Boolean  > g2) {
58          return new AndGenerator(g1, g2);
59      }
60      
61      /**
62       * Returns a Boolean Functor that produces TRUE when both input functors return TRUE for
63       * same given argument.
64       */
65      static public <T> UnaryFunctor<T,Boolean  >
66      and(UnaryFunctor<T,Boolean  > uf1, UnaryFunctor<T,Boolean  > uf2)
67      {
68          return new AndUnary<T>(uf1, uf2);
69      }
70      
71      /**
72       * Returns a Boolean Functor that produces TRUE when both input functors return TRUE for
73       * same given pair of arguments.
74       */
75      static public <T1,T2> BinaryFunctor<T1,T2,Boolean  >
76      and(BinaryFunctor<T1,T2,Boolean  > uf1, BinaryFunctor<T1,T2,Boolean  > uf2)
77      {
78          return new AndBinary<T1,T2>(uf1, uf2);
79      }
80  
81  
82      /**
83       * Returns a generator that evaluates the <tt>test</tt> and, when true, evaluates the
84       * <tt>trueFn</tt> and returns the results.  When the <tt>test</tt> is false, the
85       * generator returns <tt>null</tt>.
86       */
87      static public <R> Generator<R> conditional(Generator<Boolean  > test, Generator<R> trueFn) {
88          return new ConditionalGenerator<R>(test, trueFn, new Constant<R>(null));
89      }
90  
91      /**
92       * Returns a generator that evaluates the <tt>test</tt> and, when true, evaluates the
93       * <tt>trueFn</tt> and returns the results.  When the <tt>test</tt> is false, the
94       * generator evaluates <tt>falseFn</tt> and the returns the results
95       */
96      static public <R> Generator<R>
97      conditional(Generator<Boolean  > test, Generator<R> trueFn, Generator<R> falseFn)
98      {
99          return new ConditionalGenerator<R>(test, trueFn, falseFn);
100     }
101 
102     /**
103      * Returns a functor that evaluates the <tt>test</tt> and, when true, evaluates the
104      * <tt>trueFn</tt> and returns the results.  When the <tt>test</tt> is false, the
105      * functor returns <tt>null</tt>.  Both functors receiv the same argument when evaluated.
106      */
107     static public <T,R> UnaryFunctor<T,R>
108     conditional(UnaryFunctor<T,Boolean  > test, UnaryFunctor<T,R> trueFn)
109     {
110         return new ConditionalUnary<T,R>(test, trueFn, new ConstantUnary<T,R>(null));
111     }
112 
113     /**
114      * Returns a functor that evaluates the <tt>test</tt> and, when true, evaluates the
115      * <tt>trueFn</tt> and returns the results.  When the <tt>test</tt> is false, the
116      * functor evaluates <tt>falseFn</tt> and the returns the results.  Both functors
117      * that are evaluated receive the same pair of arguments.
118      */
119     static public <T,R> UnaryFunctor<T,R>
120     conditional(UnaryFunctor<T,Boolean  > test, UnaryFunctor<T,R> trueFn, UnaryFunctor<T,R> falseFn)
121     {
122         return new ConditionalUnary<T,R>(test, trueFn, falseFn);
123     }
124 
125 
126     /**
127      * Returns a functor that evaluates the <tt>test</tt> and, when true, evaluates the
128      * <tt>trueFn</tt> and returns the results.  When the <tt>test</tt> is false, the
129      * functor returns <tt>null</tt>.  Both functors receive the same pair of arguments when
130      * valuated.
131      */
132     static public <T1,T2,R> BinaryFunctor<T1,T2,R>
133     conditional(BinaryFunctor<T1,T2,Boolean  > test, BinaryFunctor<T1,T2,R> trueFn)
134     {
135         return new ConditionalBinary<T1,T2,R>(test, trueFn, new ConstantBinary<T1,T2,R>(null));
136     }
137 
138     /**
139      * Returns a functor that evaluates the <tt>test</tt> and, when true, evaluates the
140      * <tt>trueFn</tt> and returns the results.  When the <tt>test</tt> is false, the
141      * functor evaluates <tt>falseFn</tt> and the returns the results.  Both functors
142      * that are evaluated receive the same pair of arguments.
143      */
144     static public <T1,T2,R> BinaryFunctor<T1,T2,R>
145     conditional(BinaryFunctor<T1,T2,Boolean  > test, BinaryFunctor<T1,T2,R> trueFn,
146                 BinaryFunctor<T1,T2,R> falseFn)
147     {
148         return new ConditionalBinary<T1,T2,R>(test, trueFn, falseFn);
149     }
150 
151     
152     /**
153      */
154     static public <R> Generator<R> constant(R value) {
155         return new Constant<R>(value);
156     }
157 
158     
159     /**
160      */
161     static public <T,R> UnaryFunctor<T,R> constantUnary(R value) {
162         return new ConstantUnary<T,R>(value);
163     }
164 
165     
166     /**
167      */
168     static public <T1,T2,R> BinaryFunctor<T1,T2,R> constantBinary(R value) {
169         return new ConstantBinary<T1,T2,R>(value);
170     }
171 
172     
173     /**
174      */
175     @SuppressWarnings  ("unchecked")
176     static public <T> UnaryFunctor<T,T> identity() {
177         return (Identity<T>) _id;
178     }
179 
180    
181     /**
182      * Returns a Boolean Generator that produces TRUE when either input generators return TRUE.
183      */
184     static public Generator<Boolean  > or(Generator<Boolean  > g1, Generator<Boolean  > g2) {
185         return new OrGenerator(g1, g2);
186     }
187 
188     
189     /**
190      * Returns a Boolean Functor that produces TRUE when either input functors return TRUE for
191      * same given argument.
192      */
193     static public <T> UnaryFunctor<T,Boolean  >
194     or(UnaryFunctor<T,Boolean  > uf1, UnaryFunctor<T,Boolean  > uf2)
195     {
196         return new OrUnary<T>(uf1, uf2);
197     }
198 
199     
200     /**
201      * Returns a Boolean Functor that produces TRUE when either input functors return TRUE for
202      * same given pair of arguments.
203      */
204     static public <T1,T2> BinaryFunctor<T1,T2,Boolean  >
205     or(BinaryFunctor<T1,T2,Boolean  > uf1, BinaryFunctor<T1,T2,Boolean  > uf2)
206     {
207         return new OrBinary<T1,T2>(uf1, uf2);
208     }
209 
210 
211     /**
212      */
213     @SuppressWarnings  ("unchecked")
214     static public <T1,T2> BinaryFunctor<T1,T2,T1> project1st() {
215         return _proj1;
216     }
217 
218     
219     
220     /**
221      */
222     @SuppressWarnings  ("unchecked")
223     static public <T1,T2> BinaryFunctor<T1,T2,T2> project2nd() {
224         return _proj2;
225     }
226 }
227 
228
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