[Haskell-cafe] Safe lens?

[Edward Kmett]

Actually Control.Lens.Getter doesn't use TH. The issue is more that it
depends on some modules I didn't flag as Trustworthy and which require some
more high-falutin type system extensions that GHC isn't happy about
treating as Safe. I'll try adding a few Trustworthy flags.

It previously was treated as Trustworthy or SafeInfered throughout.

Somewhere along the way I must have toggled on an extension and broken that
property.

-Edward

On Mon, Oct 29, 2012 at 1:14 PM, Petr P <petr.mvd at gmail.com> wrote:

>   Hi
>
> I believe the reason is that it uses TemplateHaskell for automatic
> derivation of labels. And TemplateHaskell is of course unsafe, since
> it could convert your code into something entirely different.
>
>   Best regards,
>   Petr Pudlak
>
> 2012/10/29 Greg Fitzgerald <garious at gmail.com>:
> > Why are getters from the 'lens' package unsafe?  Is there a subset
> > like Data.Label.Pure from 'fclabels' that can be imported safely?
> >
> >
> > $ cat a.hs
> > {-# LANGUAGE Safe #-}
> >
> > import Control.Lens.Getter
> >
> > main = print 123
> >
> > $ runghc a.hs
> >
> > a.hs:3:1:
> >     Control.Lens.Getter: Can't be safely imported!
> >     The module itself isn't safe.
> >
> >
> > Thanks,
> > Greg
> >
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