Re: Gee Functional iterators

[Martin DeMello <martindemello gmail com>]

On Tue, Jul 13, 2010 at 9:50 PM, Maciej Piechotka <uzytkownik2 gmail com> wrote:
>
> Important:
>    Iterable<G>
>       - A fold(A ()(A, G), A)  or A foldl(A ()(A, G), A) - Left fold.
> Can be implemented in terms of Iterable (I shown it in previous e-mail)
>       - Iterator<A> scan(A ()(A, G), A) or Iterator<A> scanl(A ()(A,
> G), A) - as fold but returns partial results in iterator
>       - Iterator<G> filter(boolean ()(G)) - returns iterator skipping
> elements for which predicate does not hold
>    BidirIterable<G>
>       - A rfold(A ()(G, A), G) or A foldr(A ()(G, A), A) - Right fold
>       - BidirIterator<A> rscan(A ()(A, G), A) or Iterator<A> scanr(A
> ()(A, G), A) - as scan but goes from end.
>    Iterable<G> (some of them. Probably should return the 'self' type)
>       - Iterable<A> map(A ()(G))
>    Iterator<G> or Iterable<G> (I assume iterator)
>       - Iterator<(G, A)> zip(Iterator<A>) - combines elements from both
> iterators as they go
>       - Iterator<A> zipWith(A ()(G, B), Iterator<G>) - combine elements
> from both iterators puts them into function and returns the
>
> (+ zip3/4/5 etc.)
>
> Haskell utils (make code nice but they aren't strictly so useful. Often
> can be simply extention of previous):
>  Iterable<G>:
>     - boolean all (boolean ()(A)) - returns true if predicate is true
> for each element of collection
>     - boolean any (boolean ()(G)) - similar to previous
>     - Iterator<G> drop(int) - returns iterator skipping n first elements
>     - Iterator<G> dropWhile(boolean G()) - skips elements from the
> beginning  which hold the predicate
>     - Iterator<G> take(int) - last element is n-th element (or earlier)
>     - Iterator<G> takeWhile(boolean G()) - iterator returns element
> when it holds predicate
>  Iterator<G>:
>     - void skip(int) - skip n elements (moves iterator forward)
>     - void skipWhile(bool ()(G)) - skip elements from the beginning
> that follow the predicate (moved iterator forward)
>  Utils class??? Not needed in non-pure language?
>     - Iterator<A> execute(Iterator<A ()>)

Adding:

If we're working with external iterators, some collection methods
would be nice to have too:

void collect(Collection<G>) - iterates through the iterator and builds
up a collection
void partition(boolean()(G), Collection<G>, Collection<G>) -
partitions the iterable into two collections, based on a predicate

And I'd like to have a "reshape" operator that returns an iterator
over a list of iterators that start at every nth element and iterate
over the next n elements, but I don't know how practical that would
be. Use case is if you have a collection of m*n elements that you want
to treat as a 2D collection of m rows of n columns each, so you could
say

foreach (ListIterator<int> row in m.every(n)) {
  foreach (int element in row) {
    ...
  }
}

martin