[Haskell-cafe] Lenses and Nested Maps

[Michael Sloan]

Hi Henry,

Yes, the "ix" function traverses into particular keys of map-like
structures https://www.stackage.org/haddock/lts-13.25/lens-4.17.1/Control-Lens-At.html#v:ix

So, (s & ix "bob" . ix 6 .~ 'c') will yield a modified Map with 'b'
changed to 'c'.

-Michael

On Mon, Jun 17, 2019 at 9:45 PM Henry Laxen <nadine.and.henry at pobox.com> wrote:
>
> Hi Cafe,
>
> Suppose I have:
>
> s :: Map String (Map Int Char)
> s =  M.fromList [("alice", M.fromList [(5,'a')]), ("bob", M.fromList [(6,'b')])]
>
> Is there any way to modify the 'b' entry easily using lenses?
>
> Thanks in advance.
> Best wishes,
> Henry Laxen
>
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