Records in Haskell

[AntC]

wren ng thornton <wren <at> freegeek.org> writes:

> >
> > That's what SORF does: the String Kind
> >
> > No proposal is using a _type_-level string. Barney's confused you.
> 
> I was under the impression that all the working proposals were using the 
> Has class, ...

Yes, but:

> a la:
> 
>      someFunction :: Has "name" a => a -> Foo
>      someFunction x = ... (name x) ...
> 

No! Have you read any of the proposals? Which bit of your anatomy did you use?

Note that that syntax is not valid H98. Also note that the `Has` class uses 
three arguments, and in a different sequence to what you show.

That syntax (with 3 args present) turns up in two places:
1. SPJ's SORF proposal
2. Barney Hilken's postings. Please ignore them, is all I can say.
   Neither I nor SPJ had anything to do with them.

The DORF syntax is:

      someFunction :: Has r Proxy_name t => r -> t

I prefer the sugar, which is the same for SORF and DORF (SPJ invented it, I 
stole it unashamedly):

      someFunction :: r{ name :: t } => r -> t

The difference between the desugarring is crucial:
- SORF desugars to a String Kind -- hence Has r "name" t => ...
    the "name" in quotes represents a String Kind

- DORF desugars to a (proxy) type, not some new-fangled Kind
     Has r Proxy_name t => ...
  That is H98 (with multi-param type classes).

I propose we use the sugar, so that the implementor can decide how to, um, 
implement.

> modulo the debate about the value-level syntax for records, and modulo 
> the debate about whether Has should be exposed to users or hidden inside 
> GHC. Is this no longer the case?

Was _never_ the case, you've been paying too much attention to the wrong 
postings. Look at the wiki pages: that's why I posted it.

I repeat: nobody is using a "type-level string". You (or someone) is making it 
up.

This is beginning to exasperate me. Read the wikis: can you see "type-level 
string"? Certainly not on the DORF pages, I'm pretty sure not on the SORF 
pages. If you find it somewhere else, tell me and I'll get it changed.

AntC