I had a similar question a while back, and I've been wondering why there isn't a nicer way to combine fine grained lenses. It could be used to create law-breaking lenses, but it instead gets implemented manually each time. Perhaps some sort of typeclass or GADT arrangement could be used to define a 'basis' of an object consiting of lenses which are independent, so setting twice works fine. Actually, I think an Iso' with a tuple would be sufficient to define this. On Mon, Nov 4, 2013 at 3:04 PM, Dan Burton wrote:

There's not really a "smarter" way to do it, but there is a "prettier" way:

foo & a .~ "String" & b .~ [1,2,3] & c .~ 'c' & d .~ 4

-- Dan Burton

On Mon, Nov 4, 2013 at 2:51 PM, felipe zapata wrote:

...

Dear Haskellers,

let's suppose I have the following lenses

data Foo = Foo { _a :: String _b :: [Double] _c :: Vector Double _d :: Int .............. (more fields) _z :: Double }

Now, I want to update fields a,b,c and d without changing the rest. What is the functional way of doing it ?

Surely there a function smarter than

set a "String" . set b [1,2,3] . set c <1,2,3> . set d 4 $ foo

can some please help me with it?

Thanks in advance,

Felipe Z.

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