(I sent this to 'libraries' but Kim-Ee suggested adding Café, where so many 
smart people hang out.)


Some of you will know that I've promised to give a talk about Edward's lens 
library<http://hackage.haskell.org/package/lens> at the Haskell 
Exchange<http://skillsmatter.com/event/scala/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 

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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