Virtual package for enabling the ctypes.foreign subpackage

ctypes-foreign is just a virtual OPAM package that determines whether the foreign subpackage should built as part of ctypes. In order to actually get the ctypes package, you should also:

opam install ctypes ctypes-foreign

You can verify the existence of the ocamlfind subpackage by:

ocamlfind list | grep ctypes

Which should output something like:

ctypes              (version: 0.4.1)
ctypes.foreign      (version: 0.4.1)
ctypes.foreign.base (version: 0.4.1)
ctypes.foreign.threaded (version: 0.4.1)
ctypes.foreign.unthreaded (version: 0.4.1)
ctypes.stubs        (version: 0.4.1)
ctypes.top          (version: 0.4.1)