exception handling - System.TypeInitializationException in a match constructor -

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i trying discriminated union type string in f# (4.0, vs2015). code looks this:

type fooorbar =foo | bar let fooorbarfromstring str =     match str      | "foo" -> foo     | "bar" -> bar     | _ -> raise (system.argumentexception("invalid input"))

the problem is, if default condition triggered, , exception raised, argument exception wrapped in system.typeinitializationexception. ex: 

[<entrypoint>] let main argv =      let result = fooorbarfromstring "baz"  unhandled exception of type 'system.typeinitializationexception' occurred in project.exe

further complicating things, vs2015 debugger chokes , shows "source not available". inspecting inner exception in locals view can see going on.

is there better way of setting errors in input data don't make debugging massive pain?


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