Scheme: https://itunes.apple.com/us/app/gambit-repl/id434534076
OCaml: https://itunes.apple.com/us/app/ocamlexample/id396515573
Python: https://itunes.apple.com/us/app/python-3.3-for-ios/id5779112...
Codea (LUA): https://itunes.apple.com/us/app/codea/id439571171
What restricts these apps from being awesome is that they cannot download source code or accept source code pushed to them from other apps. Cut-n-paste is the only way to transfer existing code.
The Python app can download arbitrary data with nothing more than a simple urllib call. Feed it into eval, and you're done.
http://n4g.com/news/607824/apple-approves-manomios-c64-2-0-a...