Status update on overloaded records work?

AntC anthony_clayden at
Tue Oct 15 21:41:52 UTC 2013

> Johan Tibell <johan.tibell at ...> writes:
> I'm curious about the current status of the overloaded records work.

Hi Johan, I think Adam has documented as he's gone along:
(And that points to implementation notes.)

I'll leave Adam/Simon to comment more fully, but from my point of view as 
an observer with some 'skin in the game' ...

> Is the design the same as when the project started?

- Higher-Ranked types can't be supported
  -- and SPJ's initial proposal put a lot of weight on them.
  There's an easy (IMO) work-round;
  but it does compromise backward compatibility.
+ Type changing update _is_ supported (with limits)
  I think that was a justified trade-off for H-R types.
+ Adam has been able to support Lenses.

- (What I was hoping for but didn't get.)
  No compiler flag to suppress creating selector functions.
  This would have allowed records to be declared re-using the same name;
  but left it entirely to the developer as to how to access them.
  (I was trying to promote the TH and/or Lenses cottage industries.)

> Did we manage to keep the types simple?

I guess simplicity is in the eye of the beholder ;-)
For 'gettable' fields, the sugar is as per SPJ's suggestion.
There isn't sugar for updating.

The un-sugared types are pretty gnarly.
I suspect that'll mean obscure and confusing error messages.


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