Final call for GHC String Interpolation proposal!

Has there been any thought on how to format things more nicely? I mean things like width of a field, left/right justified, number of decimals for a float, etc. I think we could make something simple and nice, but we should do it now, before everyone invents their own way of doing it.

For instance data LAdj a = LAdj Int a instance Interpolate a => Interpolate (LAdj a) where interpolate (LAdj n a) = ... interpolate a ... pad to get width n ...