Records in Haskell

AntC anthony_clayden at
Fri Jan 27 01:18:52 CET 2012

Ryan Newton <rrnewton <at>> writes:

> I admit I'm a big fan of polymorphic extension.  But I don't love it enough 
for it to impede progress!  
> Regarding extension:  In trying to read through all this material I don't 
see a lot of love for "lacks" constraints a la TRex.  
> Cheers,
>   -Ryan
Hi Ryan, I think the "lacks" constraint is sadly misunderstood, and in fact 
something like it will be needed eventually.

[Weird! somewhere between gmaniac and pipermail, half my post went missing: I 
was only just warming up this far. Try again ... again ...]

(If anybody who knows the internals of Hugs/TRex is listening, it would be 
great to get confirmation of the following.)

As you say, it relates to whatever might happen for polymorphic records, so is 
outside the scope of what SPJ is trying to address in this thread.

On the other hand, let's try to avoid developing an approach for 'Records in 
Haskell' that has to be undone when/if we get more polymorphic.

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