PLT Scheme’s R6RS support does not conform with the standard in several known ways:
This difference can be made visible using dynamic-wind. According to R6RS, the following program should print “in” and “out” twice, but each prints once using PLT Scheme:
Along similar lines, continuation capture and invocation within an exception handler is restricted. Unless the exception is raised through raise-continuable, a handler can escape only through a continuation that is a tail of the current continuation, and a continuation captured within the handler cannot be invoked after control escapes from the raise.
The initial exception handler does not return for non-&serious conditions, but raise and raise-continuable both install an uncaught-exception handler (via parameterize and uncaught-exception-handler) to one that returns for non-&serious conditions.
Inexact numbers are printed without a precision indicator, and precision indicators are ignored on input (e.g., 0.5|7 is read the same as 0.5).