Re: We need to add role annotations for 7.8

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On Mon, Mar 24, 2014 at 10:14 AM, Mark Lentczner
<[email protected]>wrote:

> On Fri, Mar 14, 2014 at 2:36 AM, Johan Tibell <[email protected]>wrote:
>
>> I'm quite worried about this change though. I thought the default rolefor data type was nominal, as that's the safe default. *If
>> the default is representational, every package author will need to be aware
>> of this feature and update their packages.* That's quite a high cost.
>>
>
> On Fri, Mar 14, 2014 at 6:00 AM, Brandon Allbery <[email protected]>
>  wrote:
>
> *Nominal default breaks everything that uses newtype deriving and doesn't
>> have role annotations, doesn't it?* Representational default means
>> things behave in 7.8 as they did in earlier GHCs.
>>
>
> Am I reading these pair of statements correctly? It seems to imply to me
> that *every* parameterized type that uses a type constraint on a
> parameter *must* be reviewed and possibly annotated to work correctly,
> one way or the other!
>

No; if the default is representational, everything works as it did in
earlier versions, potential bugs/unsafety and all. If the default is
immediately switched to nominal, *then* every affected type must be
reviewed immediately. My counter-proposal was to have 7.8 default to
representational to give library maintainers a release cycle to add the
necessary annotations, then switch the default to nominal in 7.10 to get
the additional safety.

-- 
brandon s allbery kf8nh                               sine nomine associates
[email protected]                                  [email protected]
unix, openafs, kerberos, infrastructure, xmonad        http://sinenomine.net

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<div dir=3D"ltr"><div class=3D"gmail_extra"><div class=3D"gmail_quote">On M=
on, Mar 24, 2014 at 10:14 AM, Mark Lentczner <span dir=3D"ltr">&lt;<a href=
=3D"mailto:[email protected]" target=3D"_blank">mark.lentczner@gmail=
.com</a>&gt;</span> wrote:<br>
<blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p=
x #ccc solid;padding-left:1ex"><div dir=3D"ltr"><div class=3D"gmail_extra">=
On Fri, Mar 14, 2014 at 2:36 AM, Johan Tibell <span dir=3D"ltr">&lt;<a href=
=3D"mailto:[email protected]" target=3D"_blank">[email protected]=
</a>&gt;</span> wrote:<br>
</div><div class=3D"gmail_extra"><div class=3D"gmail_quote"><div class=3D""=
><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border=
-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;=
padding-left:1ex">


<div dir=3D"ltr"><div>I&#39;m quite worried about this change though. I tho=
ught the default <span>role</span> for data type was nominal, as that&#39;s=
 the safe default. <b>If the default is representational, every package aut=
hor will <span>need</span> to be aware of this feature and update their pac=
kages.</b> That&#39;s quite a high cost.</div>




</div><div></div></blockquote></div></div><br>On Fri, Mar 14, 2014 at 6:00 =
AM, Brandon Allbery=C2=A0<span dir=3D"ltr">&lt;<a href=3D"mailto:allbery.b@=
gmail.com" target=3D"_blank">[email protected]</a>&gt;</span>=C2=A0wrote:=
<div class=3D"">
<br><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;bor=
der-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:sol=
id;padding-left:1ex">

<div dir=3D"ltr"><div class=3D"gmail_extra"><div class=3D"gmail_quote"><div=
><b>Nominal default breaks everything that uses newtype deriving and doesn&=
#39;t have role annotations, doesn&#39;t it?</b> Representational default m=
eans things behave in 7.8 as they did in earlier GHCs.</div>


</div></div></div></blockquote><div><br></div></div><div>Am I reading these=
 pair of statements correctly? It seems to imply to me that <i>every</i> pa=
rameterized type that uses a type constraint on a parameter <i>must</i>=C2=
=A0be reviewed and possibly annotated to work correctly, one way or the oth=
er!</div>
</div></div></blockquote><div><br></div><div>No; if the default is represen=
tational, everything works as it did in earlier versions, potential bugs/un=
safety and all. If the default is immediately switched to nominal, *then* e=
very affected type must be reviewed immediately. My counter-proposal was to=
 have 7.8 default to representational to give library maintainers a release=
 cycle to add the necessary annotations, then switch the default to nominal=
 in 7.10 to get the additional safety.</div>
<div><br></div></div>-- <br><div dir=3D"ltr"><div>brandon s allbery kf8nh =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 sine nomine associates</div><div><a href=3D=
"mailto:[email protected]" target=3D"_blank">[email protected]</a> =C2=
=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0<a href=3D"mailto:ballbery@sinenom=
ine.net" target=3D"_blank">[email protected]</a></div>
<div>unix, openafs, kerberos, infrastructure, xmonad =C2=A0 =C2=A0 =C2=A0 =
=C2=A0<a href=3D"http://sinenomine.net" target=3D"_blank">http://sinenomine=
.net</a></div></div>
</div></div>

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