Records in Haskell

AntC anthony_clayden at
Thu Mar 1 21:52:29 CET 2012

Ian Lynagh <igloo <at>> writes:

> On Thu, Mar 01, 2012 at 07:58:42AM +0000, AntC wrote:
> > 
> > SORF's whadyoumaycalls are at the Kind level. (I'm not opposed to them 
> > they're new-fangled, I'm opposed because I can't control the namespace.)
> I haven't followed everything, so please forgive me if this is a stupid
> question, but if you implement this variant of SORF:
> then do you get the behaviour of SORF when using field names starting
> with a lower-case letter, and DORF when they start with an upper-case
> letter?
> Thanks
> Ian

And you get "In my opinion, this is ugly, since the selector can be either a 
type name or a label and the semantics are nonsame. Rather, we need scoped 
instances." [SPJ]

So if we open the gate for "ugly", do we also open it for "hacks" and 
for "unscalable"?

Then we also have a solution for updating higher-ranked typed fields.

I guess this is all for decision by the implementors.

If we need to go into scoped instances, I'd be really scared -- that seems 
like a huge, far-reaching change, with all sorts of opportunity for mysterious 
compile fails and inexplicable behaviour-changing from imports.

I have some creative ideas for introducing overlapping instances; shall I run 
them up the flagpole as well?


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