HomFunctor


1   package JSci.maths.categories;
2   
3   /**
4   * The HomFunctor class encapsulates the hom-bifunctor.
5   * @version 1.0
6   * @author Mark Hale
7   */
8   public class HomFunctor extends Object   implements Bifunctor {
9           private Category cat;
10          /**
11          * Constructs the hom bifunctor for a category.
12          */
13          public HomFunctor(Category c) {
14                  cat=c;
15          }
16          /**
17          * Maps two objects to another.
18          */
19          public Object   map(Object   a,Object   b) {
20                  return cat.hom(a, b);
21          }
22          /**
23          * Maps two morphisms to another.
24          */
25          public Category.Morphism map(Category.Morphism m, Category.Morphism n) {
26                  return new HomMorphism(m, n);
27          }
28          private class HomMorphism implements Category.Morphism {
29                  private Category.Morphism in,out;
30                  public HomMorphism(Category.Morphism m, Category.Morphism n) {
31                          in=m;
32                          out=n;
33                  }
34                  public Object   domain() {
35                          return cat.hom(in.codomain(), out.domain());
36                  }
37                  public Object   codomain() {
38                          return cat.hom(in.domain(), out.codomain());
39                  }
40                  public Object   map(Object   o) {
41                          return in.compose((Category.Morphism)o).compose(out);
42                  }
43                  public Category.Morphism compose(Category.Morphism m) {
44                          HomMorphism hm=(HomMorphism)m;
45                          return new HomMorphism(hm.in.compose(in), out.compose(hm.out));
46                  }
47          }
48  }
49  
50
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