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haskell - How to use the singletons library to define a HasRep instance for existentially quantified types?

I'd like to use existentially sized image windows for a couple of reasons:

  • I'd like to pack different size windows into the same list.
  • I'd like to make a Zip instance for my window type.

I'm using this code to do this:

#xA;

Now, I need to make a HasRep instance for my SomeWind type:

#xA;

I have a nagging hunch that I ought to be able to use the singletons library to help me replace the "???" above with a correct definition, but I can't figure out how.

Can anyone help?


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