It always struck me as odd that many programming languages have standard printers that will output any data structure expressible in the language, but they don'

It always struck me as odd that many programming languages have standard printers that will output any data structure expressible in the language, but they don't have accompanying readers - this forces one to roll one's own or use a completely separate serialization technique. This is useful even when not in a homoiconic language for day-to-day tasks.