My colleagues and I use OCaml to create the iOS apps we sell. Everything is encoded in OCaml, including a graphical interface. However, making OCaml fully linked to Cocoa Touch will be a very big task, so we will focus on creating the parts we need. It is definitely possible (and really nice) to use OCaml to create real GUIs, but it will take some serious support or quite a lot of community effort to get a really comfortable environment. (If you are interested in our efforts, follow the link in my profile.)
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