[ann] bidirectional iterator 0.8

[Simon Strandgaard]

I am pleased to announce the release of version 0.8 of my
Bidirectional Iterator package.


download as TGZ:
http://rubyforge.org/frs/download.php/703/iterator-0.8.tar.gz

download as ZIP:
http://rubyforge.org/frs/download.php/704/iterator-0.8.zip

documentation:
http://aeditor.rubyforge.org/iterator/



What Is It?
===========

A bunch of external iterators, which both can go forward
and backwards. You may already know iterators from Java.
The main methods are #next, #has_next? and #current.
Its carefully unittested and is being used by my regexp
engine where it indirectly is being exercised by +2000 tests.



Changes Since Last
==================

For my regexp engine I needed primitives to iterate through
unicode strings (UTF8, UTF16BE, UTF16LE), both forward and
backwards. You never know when you need to search backwards
through an huge UTF8 file. I have putted much effort into
ensuring that decoding are robust to malformed data, so
when encountering malformed data we doesn't eat bytes of the
next maybe valid codepoint. Also when doing backwards
decoding its still robust to malformed data.

Talking about File.. I have also added an iterator which
can traverse through a file. Forward and backwards.

The interface is still the same.



Some Examples
=============

#
# example 1. map on String.each_line
#
require 'iterator'
str = %w(a b c).join("\n")
iterator = Iterator::Continuation.new(str, :each_line)
result = iterator.map{|i|"<<#{i}>>"}
iterator.close
p result # ["<<a\n>>", "<<b\n>>", "<<c>>"]


#
# example 2. multiway each
#
require 'iterator'
data_a = %w(a b c d)
data_b = (0..3)
ia = Iterator::Continuation.new(data_a, :each)
ib = Iterator::Continuation.new(data_b, :each)
result = []
while ia.has_next? and ib.has_next?
result << ia.current
result << ib.current
ia.next
ib.next
end
ia.close
ib.close
p result # ["a", 0, "b", 1, "c", 2, "d", 3]


#
# example 3. decode UTF8 encoded string
#
require 'iterator'
str = [1000, 50000, 40, 999, 30000].pack('U*')
byte_iterator = str.create_iterator
res = Iterator:ecodeUTF8.new(byte_iterator).to_a
p res # [1000, 50000, 40, 999, 30000]



Call For Help
=============

Do you have knowledge about Asian text-encodings: Big5, EUC, SJIS, KOI.
Then please contact me.

BTW: if you have ideas for improvement, then speak out.

 

[Martin DeMello]

# example 2. multiway each
#
require 'iterator'
data_a = %w(a b c d)
data_b = (0..3)
ia = Iterator::Continuation.new(data_a, :each)
ib = Iterator::Continuation.new(data_b, :each)
result = []
while ia.has_next? and ib.has_next?
result << ia.current
result << ib.current
ia.next
ib.next
end
ia.close
ib.close
p result # ["a", 0, "b", 1, "c", 2, "d", 3]

This suggests "higher order" iterators composed of parallel and serial
combinations of other iterators.

ic = Iterator:arallel(ia, ib) # or even ic = ia | ib
while ic.has_next?
a, b = ic.current
result << "#{a} -> #{b}"
end
ic.close

martin

 

[Simon Strandgaard]

[snip example 2]
This suggests "higher order" iterators composed of parallel and serial
combinations of other iterators.

ic = Iterator:arallel(ia, ib) # or even ic = ia | ib
while ic.has_next?
a, b = ic.current
result << "#{a} -> #{b}"
end
ic.close

Yes, I have a MultiIterator in the sample directory.
Though I never thought of naming it Parallel.. I will consider rename.
Maybe I should refine it (owner should close children) and make a full-blown
iterator out of it ?

#
# example 4. parallel iterators
#
require 'iterator'
class MultiIterator < Iterator::Base
def initialize(*iterators)
@iterators = iterators
first
end
def first; @iterators.each{|i| i.first} end
def next; @iterators.each{|i| i.next} end
def has_next?
@iterators.each{|i| return true if i.has_next? }
false
end
def current; @iterators end
end
a = %w(a b c d e).create_iterator
b = (0..4).to_a.create_iterator
i = MultiIterator.new(a, b)
while i.has_next?
ia, ib = i.current
p [ia.current, ib.current]
i.next
end
i.close
a.close
b.close


There is also Iterator::Concat

#
# example 5. concat 3 iterators
#
require 'iterator'
ary1 = "Hell".split(//).to_a
ary2 = "O wO".split(//).to_a
ary3 = "rld!".split(//).to_a
i1 = ary1.create_iterator
i2 = ary2.create_iterator
i3 = ary3.create_iterator
iterator = Iterator::Concat.new([i1, i2, i3])
ary2.map!{|i|i.swapcase}
puts iterator.to_a.join #-> Hello World!


Thanks Martin for the Parallel name... I will add it to my todo list.