[Haskell-cafe] ANNOUNCE: lenses -- Simple Functional Lenses

Martijn van Steenbergen martijn at van.steenbergen.nl
Thu Sep 3 05:50:47 EDT 2009

Job Vranish wrote:
> A simple but powerful implementation of function lenses (aka functional 
> references, accessors, etc..).

Nice! I will definitely give it a whirl when I pick up my MUD again. I'm 
currently using accessors there. I see your functions are limited to use 
in the state monad--you're right, I've never used accessors outside of a 
state monad yet.

I'm somewhat sad that you didn't capture lenses in a datatype, because 
it is such a nice example of a Category instance. I would like to see 
how to compose lenses to access deeper fields--I use nested data 
structures and would like to modify fields that are hidden deeper in the 
state. Can you perhaps add an example to show that?



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