[R6RS] R5RS-compliant mode

[William D Clinger]

Mike Sperber, on behalf of Scheme 48, is the only one who has answered
my question asking how to run each of the major implementations we
represent in its maximally R5RS-compliant mode.

On behalf of Larceny v0.50, I'll report that its maximally R5RS-compliant
mode is obtained by evaluating (compiler-switches 'standard).

I am about to teach a course in which students may use any R5RS-compliant
implementation of Scheme but, of the implementations I have tried, only
Scheme 48 and Larceny appear to comply with R5RS section 1.3.1:

  It is required that every implementation of Scheme support
  all features that are not marked as being _optional_.
  Implementations are free to add extensions, provided the
  extensions are not in conflict with the language reported
  here.  In particular, implementations must support a mode
  that preempts no lexical conventions of this report.

I'm still hoping you folks will tell me differently.

Will