Plain Data.Set.toList doesn't seem to guarantee a order, and it would be unfortunate to get different serializations of a Set depending on how it was constructed.
./ allows an Object heirarchy to be traversed without parsing anything. If any of the path components is missing or the wrong type, it returns Missing.
This improves performance on the tweet data set by between 10% and 50%, depending on the input.
We can now convert most types deriving Data. Also, change the parsing code from being based on Applicative to using an efficient continuation-based Parser type, with a Result type signalling the result.