[Haskell-cafe] Using 'lens' for "over"-like computation in Monad

[Nikolay Amiantov]

Thank you! I'm still lost in the forest of all lens functions and
generality, and haven't expected this signature. Can someone recommend good
reading on all the lens-related types and classes,  what they represent and
how can they be used? (interested not only in "how", but also "why")
30 авг. 2014 г. 11:20 пользователь "Benno Fünfstück" <
benno.fuenfstueck at gmail.com> написал:

> The lens operator that does this is %%~, also called `traverseOf`:
>
> λ: ("Hello", "World") & _1 %%~ (\a -> putStrLn a >> return a)
> Hello
> ("Hello","World")
>
> Also see the documentation:
> http://hackage.haskell.org/package/lens-4.4.0.1/docs/Control-Lens-Traversal.html#v:traverseOf
>
> --
> Benno
>
>
> 2014-08-30 9:44 GMT+02:00 Nikolay Amiantov <nikoamia at gmail.com>:
>
>> Hello Cafe,
>>
>> I'm trying to wrap my head around 'lens' library. My current exercise is
>> to modify something using Lens in monad. Say,
>>
>> ("Hello", "World") & _1 `myOp` (\a -> putStrLn a >> return a)
>>
>> in IO, where myOp would be of type:
>>
>> myOp :: Monad m => Lens s t a b -> (a -> m b) -> s -> m t
>>
>> Of course I can write it myself, using combination of "view" and "set":
>>
>> myOp lens f v = f (view lens v) >>= flip (set lens) v
>>
>> (have not checked this, but something like that should do), but is there
>> a more elegant way?
>>
>> Nikolay.
>>
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>>
>>
>
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