[erlang-questions] [correction] Re: Additions to lists module

Michael McDaniel <>
Thu Nov 27 00:55:51 CET 2008


On Wed, Nov 26, 2008 at 03:52:15PM -0800, Michael McDaniel wrote:
> 
>  Everyone works on different kinds of problems and has their solutions.
>  One immediate use I thought of follows.  
> 
>  Note that html_tokenise is from Joe Armstrong's www_tools-1.0 on trapexit.
> 
>  
>  {ok, H} = http:request("http://somewebsite.com") ,
>  Ht      = html_tokenise:string2toks( element(3, H) ) ,
>  Pos     = list_position:pos( Hal, {tagStart,"title"} ) ,
> 
>  {_, Title} = lists:nth( Pos+1, Hal ).
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
      Pos     = list_position:pos( Ht, {tagStart,"title"} ) ,
   {_, Title} = lists:nth( Pos+1, Ht ).


 of course, should be Ht for these

~M


> 
>  Likely there are other interesting items on a page for which I
>  would have interest.
> 
> 
> ~Michael
> 
> 
> 
> On Wed, Nov 26, 2008 at 06:31:11PM -0500, Dave Smith wrote:
> >    But I do agree with you on the pos function. I don't think I would uses
> >    it. Presumably one would want to do something with the position after
> >    retrieving it, and this would probably mean using it in a function that
> >    traverses a list a second time.
> >    It would be more appropriate in a module like array.
> > 
> >    2008/11/26 Dave Smith <[1]dave.smith.to@[2]gmail.com>
> > 
> >    2008/11/26 Mazen Harake <[3]>
> > 
> >      What is the idea behind pos?
> >      Curious because I have never been in a situation where I need to
> >      know
> >      the actual position of an element since I always assume that the
> >      order
> >      in a list is always undefined. Perhaps I missed something... do you
> >      have
> >      a practical example?
> >      /M
> > 
> >      I'm not following. Lists are ordered and in many cases order is
> >      meaningful.  Otherwise you would never have reason to reverse a
> >      list.
> >      There are many functions in the lists module where the result is
> >      dependant on the lists order, and there is precedence for functions
> >      like foldlwhile; examples (takewhile/2, dropwhile/2, splitwith/2)
> > 
> > References
> > 
> >    1. http://dave.smith.to/
> >    2. http://gmail.com/
> >    3. mailto:
> 
> > _______________________________________________
> > erlang-questions mailing list
> > 
> > http://www.erlang.org/mailman/listinfo/erlang-questions
> 
> -- 
> Michael McDaniel
> Portland, Oregon, USA
> http://autosys.us
> 
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