[Haskell-cafe] RFC: functor-classes-compat

Oleg Grenrus oleg.grenrus at iki.fi
Tue Dec 13 19:38:07 UTC 2016

On 13.12.2016 21:24, David Feuer wrote:
> On Dec 13, 2016 1:26 PM, "Oleg Grenrus" <oleg.grenrus at iki.fi
> <mailto:oleg.grenrus at iki.fi>> wrote:
>     I'm not sure we want `transformers`  to depend on `containers` either,
>     not even mentioning `vector` and `unordered-containers`. Also
>     there are
>     people stuck with `transformers-0.4` (GHC 7.10).
> Good point, although practically speaking, containers currently
> *can't* depend on transformers, because transformers is not currently
> a GHC boot package. There'll probably be room for your compat package
> for a while, but you'll have to chase those bounds :-/.
transformers *is* boot package, `ghc` package depends on transformers
directly (since GHC 7.6):


$ ghc-pkg describe ghc
    array- base- binary- bytestring-
    containers- directory- filepath-
    ghc-boot-8.0.1 ghci-8.0.1 hoopl- hpc-
    process- template-haskell- time-
    transformers- unix-

>     >     Current implementations are naive, but more obviously correct.
>     >
>     > More than what?
>     It seems that implementation for Data.Map is indeed "check size,
>     compare
>     lists", but e.g for vector it uses streaming framework to make things
>     fuse, I still use "check size, compare lists" approach.
> I believe the only containers structures with non-boring instances of
> any of those classes are Data.IntMap, Data.IntSet, and Data.Tree.
IntSet is :: *

> Side question: why doesn't Read1 have the ReadPrec-based methods that
> Read does?

I have been wondering the same

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