Enumeration<A> class / enumerators Library / Dart Documentation

Enumeration<A> class

An enumeration of finite parts of A.

class Enumeration<A> extends IterableBase<A> {
 Thunk<LazyList<Finite<A>>> thunk;

 Enumeration(this.thunk);
 factory Enumeration.empty() =>
     new Enumeration(
         new Thunk(() => new LazyList.empty()));
 factory Enumeration.singleton(A x) =>
     new Enumeration(
         new Thunk(() => new LazyList.singleton(new Finite.singleton(x))));
 factory Enumeration.fix(Enumeration f(Enumeration)) {
   final enumeration = new Enumeration(null);
   final result = f(enumeration);
   enumeration.thunk = result.thunk;
   return result;
 }

 LazyList<Finite<A>> get parts => thunk.value;

 A operator [](int i) {
   var ps = parts;
   var it = i;
   while (true) {
     if (ps.isEmpty) throw new RangeError(i);
     if (it < ps.head.length) return ps.head[it];
     it = it - ps.head.length;
     ps = ps.tail;
   }
 }

 Iterator<A> get iterator => parts.expand((f) => f).iterator;

 static LazyList<Finite> _zipPlus(LazyList<Finite> xs, LazyList<Finite> ys) =>
     (xs.isEmpty || ys.isEmpty)
         ? xs + ys
         : new LazyList.cons(xs.head + ys.head,
                             () => _zipPlus(xs.tail, ys.tail));

 /**
  * Disjoint union (it is up to the user to make sure that operands are
  * disjoint).
  */
 Enumeration<A> operator +(Enumeration<A> e) =>
     new Enumeration<A>(
         new Thunk(() => _zipPlus(this.parts, e.parts)));

 /**
  * [Enumeration] is a functor.
  */
 Enumeration map(f(A x)) =>
     new Enumeration(
         new Thunk(() => parts.map((p) => p.map(f))));

 /**
  * [: _reversals([1,2,3,...]) :] is [: [[1], [2,1], [3,2,1], ...] :].
  */
 static LazyList<LazyList> _reversals(LazyList l) {
   go(LazyList rev, LazyList xs) {
     if (xs.isEmpty) return new LazyList.empty();
     final newrev = new LazyList.cons(xs.head, () => rev);
     return new LazyList.cons(newrev, () => go(newrev, xs.tail));
   }
   return go(new LazyList.empty(), l);
 }

 static _prod(LazyList<Finite> xs, LazyList<LazyList<Finite>> yss) {
   if (xs.isEmpty || yss.isEmpty) return new LazyList.empty();

   goX(ry) =>
       xs.tail.tails().map((fs) => _conv(fs, ry));

   goY(LazyList<Finite> ry, LazyList<LazyList<Finite>> rys()) {
     return new LazyList.cons(
       _conv(xs, ry),
       () {
         final _rys = rys();
         return _rys.isEmpty
             ? goX(ry)
             : goY(_rys.head, () => _rys.tail);
       });
   };

   return goY(yss.head, () => yss.tail);
 }

 static _conv(LazyList<Finite> xs, LazyList<Finite> ys) {
   var result = new Finite.empty();
   if (ys.isEmpty) return result;
   while(true) {
     if (xs.isEmpty) return result;
     result = result + (xs.head * ys.head);
     ys = ys.tail;
     if (ys.isEmpty) return result;
     xs = xs.tail;
   }
 }

 /**
  * Cartesian product.
  */
 Enumeration<Pair> operator *(Enumeration<A> e) =>
     new Enumeration<Pair>(
         new Thunk(() =>
             _prod(this.parts, _reversals(e.parts))));


 /**
 * [Enumeration] is an applicative functor.
 */
 Enumeration apply(Enumeration e) =>
     (this * e).map((pair) => (pair.fst as Function)(pair.snd));

 /**
  * Pays for one recursive call.
  */
 Enumeration<A> pay() => new Enumeration<A>(
     new Thunk(() =>
         new LazyList.cons(new Finite.empty(), () => this.parts)));

 toString() => "Enum $parts";
}

Extends

IterableBase<A> > Enumeration<A>

Constructors

new Enumeration(Thunk<LazyList<Finite<A>>> thunk) #

Creates a new Object instance.

Object instances have no meaningful state, and are only useful through their identity. An Object instance is equal to itself only.

docs inherited from Object

Enumeration(this.thunk);

factory Enumeration.empty() #

factory Enumeration.empty() =>
   new Enumeration(
       new Thunk(() => new LazyList.empty()));

factory Enumeration.fix(Enumeration f(Enumeration)) #

factory Enumeration.fix(Enumeration f(Enumeration)) {
 final enumeration = new Enumeration(null);
 final result = f(enumeration);
 enumeration.thunk = result.thunk;
 return result;
}

factory Enumeration.singleton(A x) #

factory Enumeration.singleton(A x) =>
   new Enumeration(
       new Thunk(() => new LazyList.singleton(new Finite.singleton(x))));

Properties

final E first #

inherited from IterableBase

Returns the first element.

If this is empty throws a StateError. Otherwise this method is equivalent to this.elementAt(0)

docs inherited from Iterable<E>

E get first {
 Iterator it = iterator;
 if (!it.moveNext()) {
   throw new StateError("No elements");
 }
 return it.current;
}

final bool isEmpty #

inherited from IterableBase

Returns true if there is no element in this collection.

docs inherited from Iterable<E>

bool get isEmpty => !iterator.moveNext();

final bool isNotEmpty #

inherited from IterableBase

Returns true if there is at least one element in this collection.

docs inherited from Iterable<E>

bool get isNotEmpty => !isEmpty;

final Iterator<A> iterator #

Returns an Iterator that iterates over this Iterable object.

docs inherited from Iterable<E>

Iterator<A> get iterator => parts.expand((f) => f).iterator;

final E last #

inherited from IterableBase

Returns the last element.

If this is empty throws a StateError.

docs inherited from Iterable<E>

E get last {
 Iterator it = iterator;
 if (!it.moveNext()) {
   throw new StateError("No elements");
 }
 E result;
 do {
   result = it.current;
 } while(it.moveNext());
 return result;
}

final int length #

inherited from IterableBase

Returns the number of elements in this.

Counting all elements may be involve running through all elements and can therefore be slow.

docs inherited from Iterable<E>

int get length {
 int count = 0;
 Iterator it = iterator;
 while (it.moveNext()) {
   count++;
 }
 return count;
}

final LazyList<Finite<A>> parts #

LazyList<Finite<A>> get parts => thunk.value;

final E single #

inherited from IterableBase

Returns the single element in this.

If this is empty or has more than one element throws a StateError.

docs inherited from Iterable<E>

E get single {
 Iterator it = iterator;
 if (!it.moveNext()) throw new StateError("No elements");
 E result = it.current;
 if (it.moveNext()) throw new StateError("More than one element");
 return result;
}

Thunk<LazyList<Finite<A>>> thunk #

Thunk<LazyList<Finite<A>>> thunk

Operators

A operator [](int i) #

A operator [](int i) {
 var ps = parts;
 var it = i;
 while (true) {
   if (ps.isEmpty) throw new RangeError(i);
   if (it < ps.head.length) return ps.head[it];
   it = it - ps.head.length;
   ps = ps.tail;
 }
}

Enumeration<A> operator +(Enumeration<A> e) #

Disjoint union (it is up to the user to make sure that operands are disjoint).

Enumeration<A> operator +(Enumeration<A> e) =>
   new Enumeration<A>(
       new Thunk(() => _zipPlus(this.parts, e.parts)));

Enumeration<Pair> operator *(Enumeration<A> e) #

Cartesian product.

Enumeration<Pair> operator *(Enumeration<A> e) =>
   new Enumeration<Pair>(
       new Thunk(() =>
           _prod(this.parts, _reversals(e.parts))));

Methods

bool any(bool f(E element)) #

inherited from IterableBase

Returns true if one element of this collection satisfies the predicate test. Returns false otherwise.

docs inherited from Iterable<E>

bool any(bool f(E element)) {
 for (E element in this) {
   if (f(element)) return true;
 }
 return false;
}

Enumeration apply(Enumeration e) #

Enumeration is an applicative functor.

Enumeration apply(Enumeration e) =>
   (this * e).map((pair) => (pair.fst as Function)(pair.snd));

bool contains(Object element) #

inherited from IterableBase

Returns true if the collection contains an element equal to element.

docs inherited from Iterable<E>

bool contains(Object element) {
 for (E e in this) {
   if (e == element) return true;
 }
 return false;
}

E elementAt(int index) #

inherited from IterableBase

Returns the indexth element.

If this has fewer than index elements throws a RangeError.

Note: if this does not have a deterministic iteration order then the function may simply return any element without any iteration if there are at least index elements in this.

docs inherited from Iterable<E>

E elementAt(int index) {
 if (index is! int || index < 0) throw new RangeError.value(index);
 int remaining = index;
 for (E element in this) {
   if (remaining == 0) return element;
   remaining--;
 }
 throw new RangeError.value(index);
}

bool every(bool f(E element)) #

inherited from IterableBase

Returns true if every elements of this collection satisify the predicate test. Returns false otherwise.

docs inherited from Iterable<E>

bool every(bool f(E element)) {
 for (E element in this) {
   if (!f(element)) return false;
 }
 return true;
}

Iterable expand(Iterable f(E element)) #

inherited from IterableBase

Expands each element of this Iterable into zero or more elements.

The resulting Iterable runs through the elements returned by f for each element of this, in order.

The returned Iterable is lazy, and calls f for each element of this every time it's iterated.

docs inherited from Iterable<E>

Iterable expand(Iterable f(E element)) =>
   new ExpandIterable<E, dynamic>(this, f);

dynamic firstWhere(bool test(E value), {Object orElse()}) #

inherited from IterableBase

Returns the first element that satisfies the given predicate test.

If none matches, the result of invoking the orElse function is returned. By default, when orElse is null, a StateError is thrown.

docs inherited from Iterable<E>

dynamic firstWhere(bool test(E value), { Object orElse() }) {
 for (E element in this) {
   if (test(element)) return element;
 }
 if (orElse != null) return orElse();
 throw new StateError("No matching element");
}

dynamic fold(initialValue, combine(previousValue, E element)) #

inherited from IterableBase

Reduces a collection to a single value by iteratively combining each element of the collection with an existing value using the provided function.

Use initialValue as the initial value, and the function combine to create a new value from the previous one and an element.

Example of calculating the sum of an iterable:

iterable.fold(0, (prev, element) => prev + element);

docs inherited from Iterable<E>

dynamic fold(var initialValue,
            dynamic combine(var previousValue, E element)) {
 var value = initialValue;
 for (E element in this) value = combine(value, element);
 return value;
}

void forEach(void f(E element)) #

inherited from IterableBase

Applies the function f to each element of this collection.

docs inherited from Iterable<E>

void forEach(void f(E element)) {
 for (E element in this) f(element);
}

String join([String separator = ""]) #

inherited from IterableBase

Converts each element to a String and concatenates the strings.

Converts each element to a String by calling Object.toString on it. Then concatenates the strings, optionally separated by the separator string.

docs inherited from Iterable<E>

String join([String separator = ""]) {
 Iterator<E> iterator = this.iterator;
 if (!iterator.moveNext()) return "";
 StringBuffer buffer = new StringBuffer();
 if (separator == null || separator == "") {
   do {
     buffer.write("${iterator.current}");
   } while (iterator.moveNext());
 } else {
   buffer.write("${iterator.current}");
   while (iterator.moveNext()) {
     buffer.write(separator);
     buffer.write("${iterator.current}");
   }
 }
 return buffer.toString();
}

dynamic lastWhere(bool test(E value), {Object orElse()}) #

inherited from IterableBase

Returns the last element that satisfies the given predicate test.

If none matches, the result of invoking the orElse function is returned. By default, when orElse is null, a StateError is thrown.

docs inherited from Iterable<E>

dynamic lastWhere(bool test(E value), { Object orElse() }) {
 E result = null;
 bool foundMatching = false;
 for (E element in this) {
   if (test(element)) {
     result = element;
     foundMatching = true;
   }
 }
 if (foundMatching) return result;
 if (orElse != null) return orElse();
 throw new StateError("No matching element");
}

Enumeration map(f(A x)) #

Enumeration is a functor.

Enumeration map(f(A x)) =>
   new Enumeration(
       new Thunk(() => parts.map((p) => p.map(f))));

Enumeration<A> pay() #

Pays for one recursive call.

Enumeration<A> pay() => new Enumeration<A>(
   new Thunk(() =>
       new LazyList.cons(new Finite.empty(), () => this.parts)));

E reduce(E combine(E value, E element)) #

inherited from IterableBase

Reduces a collection to a single value by iteratively combining elements of the collection using the provided function.

Example of calculating the sum of an iterable:

iterable.reduce((value, element) => value + element);

docs inherited from Iterable<E>

E reduce(E combine(E value, E element)) {
 Iterator<E> iterator = this.iterator;
 if (!iterator.moveNext()) {
   throw new StateError("No elements");
 }
 E value = iterator.current;
 while (iterator.moveNext()) {
   value = combine(value, iterator.current);
 }
 return value;
}

E singleWhere(bool test(E value)) #

inherited from IterableBase

Returns the single element that satisfies test. If no or more than one element match then a StateError is thrown.

docs inherited from Iterable<E>

E singleWhere(bool test(E value)) {
 E result = null;
 bool foundMatching = false;
 for (E element in this) {
   if (test(element)) {
     if (foundMatching) {
       throw new StateError("More than one matching element");
     }
     result = element;
     foundMatching = true;
   }
 }
 if (foundMatching) return result;
 throw new StateError("No matching element");
}

Iterable<E> skip(int n) #

inherited from IterableBase

Returns an Iterable that skips the first n elements.

If this has fewer than n elements, then the resulting Iterable is empty.

It is an error if n is negative.

docs inherited from Iterable<E>

Iterable<E> skip(int n) {
 return new SkipIterable<E>(this, n);
}

Iterable<E> skipWhile(bool test(E value)) #

inherited from IterableBase

Returns an Iterable that skips elements while test is satisfied.

The filtering happens lazily. Every new Iterator of the returned Iterable iterates over all elements of this.

As long as the iterator's elements satisfy test they are discarded. Once an element does not satisfy the test the iterator stops testing and uses every later element unconditionally. That is, the elements of the returned Iterable are the elements of this starting from the first element that does not satisfy test.

docs inherited from Iterable<E>

Iterable<E> skipWhile(bool test(E value)) {
 return new SkipWhileIterable<E>(this, test);
}

Iterable<E> take(int n) #

inherited from IterableBase

Returns an Iterable with at most n elements.

The returned Iterable may contain fewer than n elements, if this contains fewer than n elements.

It is an error if n is negative.

docs inherited from Iterable<E>

Iterable<E> take(int n) {
 return new TakeIterable<E>(this, n);
}

Iterable<E> takeWhile(bool test(E value)) #

inherited from IterableBase

Returns an Iterable that stops once test is not satisfied anymore.

The filtering happens lazily. Every new Iterator of the returned Iterable starts iterating over the elements of this.

When the iterator encounters an element e that does not satisfy test, it discards e and moves into the finished state. That is, it does not get or provide any more elements.

docs inherited from Iterable<E>

Iterable<E> takeWhile(bool test(E value)) {
 return new TakeWhileIterable<E>(this, test);
}

List<E> toList({bool growable: true}) #

inherited from IterableBase

Creates a List containing the elements of this Iterable.

The elements are in iteration order. The list is fixed-length if growable is false.

docs inherited from Iterable<E>

List<E> toList({ bool growable: true }) =>
   new List<E>.from(this, growable: growable);

Set<E> toSet() #

inherited from IterableBase

Creates a Set containing the elements of this Iterable.

docs inherited from Iterable<E>

Set<E> toSet() => new Set<E>.from(this);

dynamic toString() #

Returns a string representation of this object.

docs inherited from Object

toString() => "Enum $parts";

Iterable<E> where(bool f(E element)) #

inherited from IterableBase

Returns a lazy Iterable with all elements that satisfy the predicate test.

This method returns a view of the mapped elements. As long as the returned Iterable is not iterated over, the supplied function test will not be invoked. Iterating will not cache results, and thus iterating multiple times over the returned Iterable will invoke the supplied function test multiple times on the same element.

docs inherited from Iterable<E>

Iterable<E> where(bool f(E element)) => new WhereIterable<E>(this, f);