Unless you're looking for an IDE. I don't think there are any for the App Store.
LOL, good one. I would suppose an IDE would be allowed, as long as it doesn't permit testing the code on the iPad. That would involve interpretation, unless it is a compiled language. And in the latter case, there's a rule that an app can't download or install additional code as well.
I'm not sure why others are saying "not possible" for editor. An editor is just that - an editor. I'm sure they'll allow you to edit anything you'd like.
As a practical matter, there's the concern of "where are the files I am going to edit". Any good editor for iPad should allow you to edit local files, as well as access popular cloud services, and upload/download (perhaps transparently, making it LOOK like you are doing a remote-edit) using FTP, sFTP, etc.