Skip tag for single-constructor data types?

[well-typed]

Skip tag for single-constructor data types?

[edsko]

Although I suppose maybe this is by design, so that if later constructors are added things don't break? If so, perhaps some convenience function to make it easier to define such instances manually might be helpful (if the programmer knows there will not be more constructors). The library provides instances for tuples, but only up to length 7 (I'm guessing the same function that I'm proposing here could also be useful to define those tuple instances).

[dcoutts]

This is by design. Actually I'm concerned that the single-constructor-single-field data types don't have a tag. The tags are not just for multiple constructors but to allow for migrations when you change the constructor in future.

[dcoutts]

The single-constructor-single-field special case should be eliminated. Those cases should use a tag too, otherwise there's no way to change the representation later and still be able to read old files.

[bgamari]

Indeed the single-field case was eliminated in db52a11.