The F# type converter converts as follows:
https://github.com/BlueMountainCapital/FSharpRProvider/blob/master/src/RProvider/RInterop.fs
The basic idea is that the SEXP pointers used by R come in a few easily discovered flavors (at least for primitive arrays). These can be easily converted, but the lists it uses are a bit harder to work with, but again shouldn't be too hard.
https://github.com/BlueMountainCapital/FSharpRProvider/blob/master/src/RProvider/RInterop.fs
The basic idea is that the SEXP pointers used by R come in a few easily discovered flavors (at least for primitive arrays). These can be easily converted, but the lists it uses are a bit harder to work with, but again shouldn't be too hard.