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  1. import java.util.Objects;
  2. import java.util.Optional;
  3. import java.util.function.BiFunction;
  4. import java.util.function.Function;
  5. import java.util.function.Supplier;
  6. import java.util.stream.Stream;
  7.  
  8. @FunctionalInterface
  9. interface Selector<TYPE> {
  10.   Object $get(Function<TYPE, Object> function);
  11.  
  12.   @SuppressWarnings("unchecked")
  13.   public default <VALUE> VALUE get(Function<TYPE, VALUE> function) {
  14.     return (VALUE) $get(
  15.       (Function<TYPE, Object>) function
  16.     );
  17.   }
  18.  
  19.   public default TYPE from(Selector<TYPE> selector) {
  20.     throw new InternalError("Selector::from is not implemented.");
  21.   }
  22.  
  23.   public default <VALUE> TYPE with(Function<TYPE, ? extends VALUE> function, VALUE value) {
  24.     return from(f -> (f == function)
  25.       ? value
  26.       : get(f)
  27.     );
  28.   }
  29.  
  30.   public static <TYPE> Object none(Function<TYPE, Object> function) {
  31.     throw new IllegalStateException("no value");
  32.   }
  33. }
  34.  
  35. interface Cons<ELEMENT> {
  36.   public ELEMENT getElement();
  37.   public Cell<ELEMENT> getNext();
  38.   public Implementation<ELEMENT> getImplementation();
  39.  
  40.   public Cons<ELEMENT> withElement(ELEMENT element);
  41.   public Cons<ELEMENT> withNext(Cell<ELEMENT> next);
  42.   public Cons<ELEMENT> withImplementation(Implementation<ELEMENT> implementation);
  43.  
  44.   @FunctionalInterface
  45.   public interface Implementation<ELEMENT> {
  46.     public <VALUE> VALUE select(ELEMENT element, Cell<ELEMENT> next, BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil);
  47.   }
  48.  
  49.   public default <VALUE> VALUE cons(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
  50.     return getImplementation()
  51.       .select(
  52.         getElement(),
  53.         getNext(),
  54.         cons,
  55.         nil
  56.       )
  57.     ;
  58.   }
  59.  
  60.   public static <ELEMENT> Cons<ELEMENT> none() {
  61.     return $Cons.none();
  62.   }
  63. }
  64.  
  65. @FunctionalInterface
  66. interface $Cons<ELEMENT> extends Cons<ELEMENT>, Selector<Cons<ELEMENT>> {
  67.   public static <ELEMENT> Function<Cons<ELEMENT>, ELEMENT> Element() {
  68.     return Cons::getElement;
  69.   }
  70.  
  71.   public static <ELEMENT> Function<Cons<ELEMENT>, Cell<ELEMENT>> Next() {
  72.     return Cons::getNext;
  73.   }
  74.  
  75.   public static <ELEMENT> Function<Cons<ELEMENT>, Implementation<ELEMENT>> Implementation() {
  76.     return Cons::getImplementation;
  77.   }
  78.  
  79.   @Override
  80.   public default ELEMENT getElement() {
  81.     return get(Element());
  82.   }
  83.  
  84.   @Override
  85.   public default Cell<ELEMENT> getNext() {
  86.     return get(Next());
  87.   }
  88.  
  89.   @Override
  90.   public default Implementation<ELEMENT> getImplementation() {
  91.     return get(Implementation());
  92.   }
  93.  
  94.   @Override
  95.   public default Cons<ELEMENT> withElement(ELEMENT element) {
  96.     return with(Element(), element);
  97.   }
  98.  
  99.   @Override
  100.   public default Cons<ELEMENT> withNext(Cell<ELEMENT> next) {
  101.     return with(Next(), next);
  102.   }
  103.  
  104.   @Override
  105.   public default Cons<ELEMENT> withImplementation(Implementation<ELEMENT> implementation) {
  106.     return with(Implementation(), implementation);
  107.   }
  108.  
  109.   @Override
  110.   public default Cons<ELEMENT> from(Selector<Cons<ELEMENT>> selector) {
  111.     return ($Cons<ELEMENT>) selector::get;
  112.   }
  113.  
  114.   public static <ELEMENT> $Cons<ELEMENT> none() {
  115.     return Selector::none;
  116.   }
  117. }
  118.  
  119. @FunctionalInterface
  120. interface Cell<ELEMENT> {
  121.   public <VALUE> VALUE select(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil);
  122.  
  123.   public default int size() {
  124.     return select(
  125.       (element, next) -> 1 + next.size(),
  126.       () -> 0
  127.     );
  128.   }
  129.  
  130.   public default Cell<ELEMENT> first(int size) {
  131.     return Optional.of(size)
  132.       .<Cell<ELEMENT>>map(s -> select(
  133.         (element, next) -> s == 0
  134.           ? nil()
  135.           : cons(element, next.first(s - 1))
  136.         ,
  137.         Cell::nil
  138.       ))
  139.       .orElseThrow(IllegalArgumentException::new)
  140.     ;
  141.   }
  142.  
  143.   public default <ELEMENT2> Cell<ELEMENT2> map(Function<? super ELEMENT, ? extends ELEMENT2> mapper) {
  144.     return select(
  145.       (element, next) -> Cell.cons(mapper.apply(element), next.map(mapper)),
  146.       Cell::nil
  147.     );
  148.   }
  149.  
  150.   public default <ELEMENT2> Cell<ELEMENT2> flatMap(Function<? super ELEMENT, Cell<ELEMENT2>> mapper) {
  151.     return select(
  152.       (element, next) -> mapper
  153.         .apply(element)
  154.         .select(
  155.           Cell::cons,
  156.           () -> next.flatMap(mapper)
  157.         )
  158.       ,
  159.       Cell::nil
  160.     );
  161.   }
  162.  
  163.   public static <ELEMENT, VALUE> VALUE nil(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
  164.     return nil.get();
  165.   }
  166.  
  167.   public static <ELEMENT, VALUE> VALUE cons(ELEMENT element, Cell<ELEMENT> next, BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
  168.     return cons.apply(element, next);
  169.   }
  170.  
  171.   public static <ELEMENT> Cell<ELEMENT> nil() {
  172.     return Cell::nil;
  173.   }
  174.  
  175.   public static <ELEMENT> Cell<ELEMENT> cons(ELEMENT element, Cell<ELEMENT> next) {
  176.     Stream.of(
  177.       element,
  178.       next
  179.     )
  180.       .forEach(Objects::requireNonNull)
  181.     ;
  182.     return Cons.<ELEMENT>none()
  183.       .withElement(element)
  184.       .withNext(next)
  185.       .withImplementation(Cell::cons)
  186.       ::cons
  187.     ;
  188.   }
  189.  
  190.   public static void main(String... arguments) {
  191.     Cell<Integer> cell =
  192.       cons(1, cons(2, cons(3, nil())))
  193.     ;
  194.     System.out.println(nil() == nil());  // true
  195.     System.out.println(cell.size() == 3);  // true
  196.     System.out.println(cell.first(2).size() == 2);  // true
  197.   }
  198. }
  199.  
  200. public interface Main {
  201.   public static void main(String... arguments) {
  202.     Cell.main(arguments);
  203.   }
  204. }
Compilation error #stdin compilation error #stdout 0s 0KB
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Standard input is empty
compilation info 
Main.java:13: error: illegal start of type
  public default <VALUE> VALUE get(Function<TYPE, VALUE> function) {
         ^
Main.java:13: error: = expected
  public default <VALUE> VALUE get(Function<TYPE, VALUE> function) {
                 ^
Main.java:13: error: ';' expected
  public default <VALUE> VALUE get(Function<TYPE, VALUE> function) {
                  ^
Main.java:13: error: illegal start of type
  public default <VALUE> VALUE get(Function<TYPE, VALUE> function) {
                       ^
Main.java:13: error: = expected
  public default <VALUE> VALUE get(Function<TYPE, VALUE> function) {
                               ^
Main.java:13: error: illegal start of type
  public default <VALUE> VALUE get(Function<TYPE, VALUE> function) {
                                  ^
Main.java:13: error: = expected
  public default <VALUE> VALUE get(Function<TYPE, VALUE> function) {
                                           ^
Main.java:13: error: <identifier> expected
  public default <VALUE> VALUE get(Function<TYPE, VALUE> function) {
                                                ^
Main.java:13: error: ';' expected
  public default <VALUE> VALUE get(Function<TYPE, VALUE> function) {
                                                 ^
Main.java:13: error: illegal start of type
  public default <VALUE> VALUE get(Function<TYPE, VALUE> function) {
                                                       ^
Main.java:13: error: = expected
  public default <VALUE> VALUE get(Function<TYPE, VALUE> function) {
                                                                 ^
Main.java:13: error: illegal start of type
  public default <VALUE> VALUE get(Function<TYPE, VALUE> function) {
                                                                   ^
Main.java:13: error: <identifier> expected
  public default <VALUE> VALUE get(Function<TYPE, VALUE> function) {
                                                                    ^
Main.java:14: error: <identifier> expected
    return (VALUE) $get(
                 ^
Main.java:14: error: ';' expected
    return (VALUE) $get(
                  ^
Main.java:15: error: illegal start of type
      (Function<TYPE, Object>) function
                             ^
Main.java:15: error: '(' expected
      (Function<TYPE, Object>) function
                               ^
Main.java:16: error: illegal start of type
    );
    ^
Main.java:16: error: <identifier> expected
    );
     ^
Main.java:17: error: = expected
  }
  ^
Main.java:17: error: ';' expected
  }
   ^
Main.java:19: error: illegal start of type
  public default TYPE from(Selector<TYPE> selector) {
         ^
Main.java:19: error: = expected
  public default TYPE from(Selector<TYPE> selector) {
                      ^
Main.java:19: error: illegal start of type
  public default TYPE from(Selector<TYPE> selector) {
                          ^
Main.java:19: error: = expected
  public default TYPE from(Selector<TYPE> selector) {
                                   ^
Main.java:19: error: <identifier> expected
  public default TYPE from(Selector<TYPE> selector) {
                                        ^
Main.java:19: error: ';' expected
  public default TYPE from(Selector<TYPE> selector) {
                                         ^
Main.java:19: error: illegal start of type
  public default TYPE from(Selector<TYPE> selector) {
                                                  ^
Main.java:19: error: <identifier> expected
  public default TYPE from(Selector<TYPE> selector) {
                                                   ^
Main.java:20: error: = expected
    throw new InternalError("Selector::from is not implemented.");
    ^
Main.java:20: error: ';' expected
    throw new InternalError("Selector::from is not implemented.");
         ^
Main.java:20: error: <identifier> expected
    throw new InternalError("Selector::from is not implemented.");
                           ^
Main.java:20: error: illegal start of type
    throw new InternalError("Selector::from is not implemented.");
                            ^
Main.java:23: error: class, interface, or enum expected
  public default <VALUE> TYPE with(Function<TYPE, ? extends VALUE> function, VALUE value) {
         ^
Main.java:28: error: class, interface, or enum expected
  }
  ^
Main.java:30: error: class, interface, or enum expected
  public static <TYPE> Object none(Function<TYPE, Object> function) {
                ^
Main.java:32: error: class, interface, or enum expected
  }
  ^
Main.java:49: error: illegal start of type
  public default <VALUE> VALUE cons(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
         ^
Main.java:49: error: = expected
  public default <VALUE> VALUE cons(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
                 ^
Main.java:49: error: ';' expected
  public default <VALUE> VALUE cons(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
                  ^
Main.java:49: error: illegal start of type
  public default <VALUE> VALUE cons(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
                       ^
Main.java:49: error: = expected
  public default <VALUE> VALUE cons(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
                               ^
Main.java:49: error: illegal start of type
  public default <VALUE> VALUE cons(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
                                   ^
Main.java:49: error: = expected
  public default <VALUE> VALUE cons(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
                                              ^
Main.java:49: error: illegal start of type
  public default <VALUE> VALUE cons(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
                                               ^
Main.java:49: error: <identifier> expected
  public default <VALUE> VALUE cons(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
                                                ^
Main.java:49: error: = expected
  public default <VALUE> VALUE cons(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
                                                       ^
Main.java:49: error: = expected
  public default <VALUE> VALUE cons(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
                                                                    ^
Main.java:49: error: <identifier> expected
  public default <VALUE> VALUE cons(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
                                                                            ^
Main.java:49: error: <identifier> expected
  public default <VALUE> VALUE cons(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
                                                                              ^
Main.java:49: error: = expected
  public default <VALUE> VALUE cons(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
                                                                               ^
Main.java:49: error: ';' expected
  public default <VALUE> VALUE cons(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
                                                                                ^
Main.java:49: error: <identifier> expected
  public default <VALUE> VALUE cons(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
                                                                                              ^
Main.java:49: error: ';' expected
  public default <VALUE> VALUE cons(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
                                                                                               ^
Main.java:49: error: illegal start of type
  public default <VALUE> VALUE cons(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
                                                                                                    ^
Main.java:49: error: = expected
  public default <VALUE> VALUE cons(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
                                                                                                              ^
Main.java:49: error: illegal start of type
  public default <VALUE> VALUE cons(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
                                                                                                               ^
Main.java:49: error: <identifier> expected
  public default <VALUE> VALUE cons(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
                                                                                                                ^
Main.java:49: error: = expected
  public default <VALUE> VALUE cons(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
                                                                                                                         ^
Main.java:49: error: ';' expected
  public default <VALUE> VALUE cons(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
                                                                                                                              ^
Main.java:49: error: <identifier> expected
  public default <VALUE> VALUE cons(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
                                                                                                                                   ^
Main.java:49: error: ';' expected
  public default <VALUE> VALUE cons(BiFunction<? super ELEMENT, Cell<ELEMENT>, ? extends VALUE> cons, Supplier<? extends VALUE> nil) {
                                                                                                                                    ^
Main.java:50: error: illegal start of type
    return getImplementation()
    ^
Main.java:50: error: ';' expected
    return getImplementation()
                              ^
Main.java:60: error: class, interface, or enum expected
  public static <ELEMENT> Cons<ELEMENT> none() {
                ^
Main.java:62: error: class, interface, or enum expected
  }
  ^
Main.java:68: error: ';' expected
    return Cons::getElement;
               ^
Main.java:68: error: not a statement
    return Cons::getElement;
                 ^
Main.java:72: error: ';' expected
    return Cons::getNext;
               ^
Main.java:72: error: not a statement
    return Cons::getNext;
                 ^
Main.java:76: error: ';' expected
    return Cons::getImplementation;
               ^
Main.java:76: error: not a statement
    return Cons::getImplementation;
                 ^
Main.java:80: error: illegal start of type
  public default ELEMENT getElement() {
         ^
Main.java:80: error: = expected
  public default ELEMENT getElement() {
                 ^
Main.java:80: error: ';' expected
  public default ELEMENT getElement() {
                        ^
Main.java:80: error: illegal start of type
  public default ELEMENT getElement() {
                                   ^
Main.java:80: error: <identifier> expected
  public default ELEMENT getElement() {
                                    ^
Main.java:80: error: = expected
  public default ELEMENT getElement() {
                                      ^
Main.java:80: error: ';' expected
  public default ELEMENT getElement() {
                                       ^
Main.java:81: error: <identifier> expected
    return get(Element());
              ^
Main.java:81: error: <identifier> expected
    return get(Element());
                      ^
Main.java:81: error: ';' expected
    return get(Element());
                       ^
Main.java:81: error: illegal start of type
    return get(Element());
                        ^
Main.java:81: error: <identifier> expected
    return get(Element());
                         ^
Main.java:82: error: = expected
  }
  ^
Main.java:82: error: ';' expected
  }
   ^
Main.java:84: error: <identifier> expected
  @Override
           ^
Main.java:85: error: = expected
  public default Cell<ELEMENT> getNext() {
  ^
Main.java:85: error: ';' expected
  public default Cell<ELEMENT> getNext() {
        ^
Main.java:90: error: illegal start of type
  public default Implementation<ELEMENT> getImplementation() {
         ^
Main.java:90: error: = expected
  public default Implementation<ELEMENT> getImplementation() {
                 ^
Main.java:90: error: ';' expected
  public default Implementation<ELEMENT> getImplementation() {
                               ^
Main.java:90: error: <identifier> expected
  public default Implementation<ELEMENT> getImplementation() {
                                       ^
Main.java:90: error: ';' expected
  public default Implementation<ELEMENT> getImplementation() {
                                        ^
Main.java:90: error: illegal start of type
  public default Implementation<ELEMENT> getImplementation() {
                                                          ^
Main.java:90: error: <identifier> expected
  public default Implementation<ELEMENT> getImplementation() {
                                                           ^
Main.java:90: error: = expected
  public default Implementation<ELEMENT> getImplementation() {
                                                             ^
Main.java:90: error: ';' expected
  public default Implementation<ELEMENT> getImplementation() {
                                                              ^
Main.java:91: error: <identifier> expected
    return get(Implementation());
              ^
Main.java:91: error: <identifier> expected
    return get(Implementation());
                             ^
100 errors
stdout
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Standard output is empty
https://ideone.com/BNJgsE
language:
Java (HotSpot 12)
created:
10 years ago
visibility:
public

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