Simon,

I've used lenses to manipulate URIs represented as strings in a structured way, 
like:

  modify (port . iso parsePrintUri) (+10) "http://localhost:8070/index.html";

Of course using fclabels and not lens ;-)

Sebastiaan

On Oct 3, 2013, at 10:07 AM, Simon Peyton-Jones <simo...@microsoft.com> wrote:

> (I sent this to ‘libraries’ but Kim-Ee suggested adding Café, where so many 
> smart people hang out.)
>  
> Friends
>  
> Some of you will know that I’ve promised to give a talk about Edward’s lens 
> library at the Haskell Exchange in London next Wednesday (9th).  I did this 
> to give everyone (including me) a break from GHC hackery, and also to force 
> me to learn about this lens voodoo that everyone is twittering about.  Edward 
> generously gave me quite a bit of one-to-one attention last week (my hair is 
> still standing on end), but this message is to ask your help too.
> 
> Specifically, I’d like to give some compelling use-cases.   If you are using 
> the lens library yourself, could you spare a few minutes to tell me how you 
> are using it?  I expect to cover Lens and Traversal but not Prism.
>  
> The use-case everyone starts with is nested records, but I’d like to go 
> beyond that.  The next levels seem to be:
> ·         Lenses as views of data that isn’t “really there” e.g. regarding a 
> record with rectangular coordinates as having polar coordinates too.
> ·         Lenses and Traversals that focus on elements of finite maps 
> (Control.Lens.At)
>  
> What else? I’m sure you are using them in all sorts of cool ways that I would 
> never think of, and I’d love to know.
>  
> Please don’t tell me anything secret!  To give everyone the benefit I may 
> just concatenate all the replies and send to you all, so please say if you 
> don’t want me to do that with yours.
>  
> And don’t burn too many cycles on this...I don’t want to waste your time, and 
> I can always get back to you if I can’t understand what you say.  Sooner is 
> better than later...Weds is coming.
>  
> Simon “Edward’s prophet” PJ
>  
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