Actually, all the various versions of my JSON parser have converted the input to a list of characters. I wouldn't be surprised if it did in fact turn to be slow, but I see it as an optimization issue: until I have (or someone else has) a program that's actually slow because of it, then I don't know if it's a useful optimization to work on. For example, if JSON parsing were a thousand times faster if I wasn't using lists, but JSON parsing was only 0.1% of the program's total execution time, then I might not care.