[plt-scheme] Using FFI with complex structures and input/output parameters?

Thank you for your corrections and suggestions. I've applied them and
reduced again source code to help diagnosis, but the error message at
"SCardTransmit" call is still there ("zero?: expects argument of type
<real number>; given #<cpointer>"). I'm sending modified sources as
attachment to avoid breaking indentation.

Thank you for your attention.
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