I've read a few discussions/comparisons between enumerators
(internal iterators) vs. cursors (external iterators).  From
what I gather those discussions in favor of enumerators assume
the application is a simple single pass read-only processing of
all/some of the elements in a collection.  You do this a lot
with a collection and I like enumerators best for doing it. 
But when you are doing something more complex, enumerators
don't cut it.

I'm still working on some general parser classes (and a lexer
is one of these parsers) where the collection is a sequence of
characters (lexer/parser) or a sequence of tokens (parser).  I
started making my own API for accessing these, but now I'm just
going ahead and making a general cursor API.  Am I duplicating
anything else?  Here are the kinds of things you'll be able to
do with this cursor interface:

get Next/Prev/After/Before
move Next/Prev
replace Next/Prev/After/Before (optionally get what is
replaced)
delete After/Before (optionally retrieve what's deleted)
insert After/Before

get position (position could be any type of object)
set position
release position (release buffering needed for unidirection
cursor - i.e IO pipe)
buffered? - query whether there are any non-released positions

The methods above that read/write at the cursor will work on
one element at a time or a string/array/N of them. 
get/move/delete will even be able to get so many elements up to
a certain string /array of them - like gets("\n").  I'm trying
to make this have a superset of the functions in IO in addition
to handling sequences of anything.

I would hope this API could be used to access and modify a wide
variety of ordered collections - strings, arrays, files/IO,
single/double linked lists, circular buffers, text editor
buffers, etc.  It could possibly be used for unordered
collections (i.e. hashes) in a read-only manner but I see no
advantage over an enumerator in that case.

Eric


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