[MLton] should Date.{fromString,scan} allow space instead of zero?

[Stephen Weeks]

> Is there any reason not to have a ref cell in some MLton specific
> structure that lets users choose between the restrictive and liberal
> mode?

Not a bad idea.  The only reason I see is complexity of code,
documentation, and mental overhead for users of the library.  I don't
claim it's a strong reason.

> For portability nuts, it be nice to be able to test your code
> against the most restrictive reading of the Basis spec. 

True.

> I'd suggest there be one flag that controls liberal and restrictive
> mode for every useful feature that MLton supports but also deviates
> from the percise letter of the spec.

A single flag alleviates the complexity somewhat.  Although this would
be our only use of it so far (except for maybe -ieee-fp, but I think
that deserves a separate flag).