[Haskell-cafe] An idea on extensible effects (anonymous record)

[MarLinn]

>> Does this differ significantly from fclabels or the upcoming 
>> OverloadedRecordFields extension? (Aside from being purely type 
>> driven, which has problems in your example if you compose a second 
>> Int into it.)
> 1. Yes, it’s similar to OverloadedRecordFields but doesn’t force you 
> to use a label, and you may use Tagged to label a field if you want.
> 2. Yes, but again, you can use Tagged to allow same type in different 
> disguise.

I can see a potential problem because you can't hide instances. Once you 
define a Has-relationship, you can't cheaply change it. That could lead 
to conflicts, unless you hack around it with orphaned instances in a 
separate module. But you say you want to solve conflicts with tagging – 
so it would be reasonable to incorporate the tag in the class from the 
start. Which brings us back to fclabels I suppose.

MarLinn
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