Changes to primops break libraries (was Re: 7.8 Feature window)

Gregory Collins greg at
Mon Aug 26 10:56:15 CEST 2013

On Sun, Aug 25, 2013 at 9:47 PM, Simon Marlow <marlowsd at> wrote:

> On 25/08/13 20:16, Jan Stolarek wrote:
>> We really want people to use the new primops, not the wrappers
>> We do? Could you justify why we want to people to use primops?
> What I meant was, if people are already using primops we want them to use
> the new ones instead.

Please don't just break existing code!

Changing the meaning of existing names, even if those are the names you
really really want to use, is user-hostile: when the next version of GHC
comes out I'm going to have to rush to update my broken packages under time
pressure instead of just getting a deprecation warning and improving the
code at my leisure. If you reeeeallly really really want those names then
there are ways to mitigate that: do your "GHC.Prim.Compat" trick in reverse.

In any event, a 0-month deprecation cycle is far too short, even for
low-level APIs.

Gregory Collins <greg at>
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