Uses reflection provided by F# in the FSharpType namespace to translate a given System.Type object into a value of the 'a ty union type defined by https://gist.github.com/926994. From Jon Harrop's "Visual F# 2010 for Technical Computing"

type_of.fs

let rec type_of f = function
    | ty when Reflection.FSharpType.IsFunction ty ->
        let ty_arg, ty_ret = Reflection.FSharpType.GetFunctionElements ty
        Function(type_of f ty_arg, type_of f ty_ret)
    | ty when Reflection.FSharpType.IsTuple ty ->
        Tuple
            [ for ty in Reflection.FSharpType.GetTupleElements ty do
                yield type_of f ty ]
    | ty when Reflection.FSharpType.IsRecord ty ->
        Record( ty.Name,
                [ for pi in Reflection.FSharpType.GetRecordFields ty do
                    for acc in pi.GetAccessors() do
                        yield pi.Name, f acc.ReturnType ] )
    | ty when Reflection.FSharpType.IsUnion ty ->
        Union( ty.Name,
                [ for uc in Reflection.FSharpType.GetUnionCases ty do
                    let args =
                        [ for field in uc.GetFields() ->
                            f field.PropertyType ]
                    yield uc.Name, args ])
    | ty ->
        Abbrev( [ for ty in ty.GetGenericArguments() -> f ty ],
                ty.FullName);;