From: Horst <horst@...>
Date: 2003-09-17T09:33:02+09:00
Subject: Re: RAA-stream  implicit iterator maybe offbyone ?

Simon Strandgaard wrote:

> I am testing the 'stream' module..
> http://raa.ruby-lang.org/list.rhtml?name=stream
> 
> 
> Q1: I have to overload the implicitstream.at_beginning_proc
> with a offbyone value..  Why ?
> 
Because the stream is at beginning if the next forward should give the first
element in the stream which is 1 in the test case below. Thats why the
initial value of the variable x should be zero and the at_beginning_proc
should test this.

Here ist my version of the stream:

  # a stream which is aquivalent (1..5).create_stream
  def new_implicit_stream
    s = Stream::ImplicitStream.new { |s|
        x = 0
      s.at_beginning_proc = proc {x < 1}
      s.at_end_proc = proc {x == 5}
      s.forward_proc = proc {x += 1 }
      s.backward_proc = proc {|y| y = x; x -= 1; y }
    }
  end

This version passes all tests that the collection stream passes. See tests
TestStream.rb

> Q2: Is this me which is thinking wrong, or is it a design flaw
> in the 'stream' library?
>
When designing the library I also had to think more about this. Have you
read the stream-doku contained in the RGL-Library which also includes the
stream module? I regret that it is not included in tarball of the stream
module. See http://rgl.sourceforge.net/files/stream_rb.html

Cheers
Horst


> 
> I have made two methods which should return virtually the
> same stream;  [1, 2, 3, 4, 5, 6]
> 
> 
> 
> 
> server> expand -t2 test_misc.rb
> require 'test/unit'
> require 'stream'
> 
> class TestMisc < Test::Unit::TestCase
>   def mk_str16
>     (1..6).create_stream
>   end
>   def mk_str16x
>     Stream::ImplicitStream.new{|s|
>       x = 1
>       s.at_end_proc = proc {x == 6}
>       s.forward_proc = proc {x += 1}
>       s.at_beginning_proc = proc {x == 0} # todo: why is'nt it {x == 1}
>       s.backward_proc = proc {x -= 1}
>     }
>   end
>   def setup
>     @data = mk_str16.filtered{|x| x % 2 == 0}
>     @data += mk_str16x.filtered{|x| x % 2 != 0}
>   end
>   def test_toa
>     assert_equal([2, 4, 6, 1, 3, 5], @data.to_a)
>   end
>   def test_revtoa
>     assert_equal([5, 3, 1, 6, 4, 2], @data.reverse.to_a)
>   end
> end
> 
> if $0 == __FILE__
>   require 'test/unit/ui/console/testrunner'
>   Test::Unit::UI::Console::TestRunner.run(TestMisc)
> end
> server> ruby test_misc.rb
> Loaded suite TestMisc
> Started
> ..
> Finished in 0.008114 seconds.
> 
> 2 tests, 2 assertions, 0 failures, 0 errors
> server>
> 
> 
> 
> If I change the 'at_beginning_proc' to stop at '1' which I believe
> is where it should stop, then I get this error:
> 
> 
> server> ruby test_misc.rb
> Loaded suite TestMisc
> Started
> FF
> Finished in 0.009856 seconds.
> 
>   1) Failure!!!
> test_revtoa(TestMisc) [test_misc.rb:25]:
> <[5, 3, 1, 6, 4, 2]> expected but was
> <[5, 3, 6, 4, 2]>
> 
>   2) Failure!!!
> test_toa(TestMisc) [test_misc.rb:22]:
> <[2, 4, 6, 1, 3, 5]> expected but was
> <[2, 4, 6, 3, 5]>
> 
> 2 tests, 2 assertions, 2 failures, 0 errors
> server>
> 
> 
> --
> Simon Strandgaard