David Vanderson:

> For example, if your editor had a tab-width of 2:
>
> [tab][space][space]define foo()
> [space][space][tab]  "bar"
>
> My reading of the spec says this would be an error, but it would be
> especially difficult to understand, because there's no visual
> difference.  Am I missing something, or has this already been discussed
> elsewhere?

Your reading is correct, the spec defines that as an error.

I don't think it's hard to understand, though.
You're right that it would *look* the same, but it's easily
detected and diagnosed at read time.  For example,
the reference implementation produces this error message
on receiving the second line:
  Error: Inconsistent indentation

That's a fairly specific error message.  If you don't think that's
clear enough, we could even modify it further to identity exactly
what was different, e.g.:
  Error: Inconsistent indentation between '\x09  ' and '  \x09'

What worries me are common, easily-made errors that a reader or interpreter
*cannot* detect.    This isn't the case at all; just like ")" with no matching "(",
this is easily detected and diagnosed.

--- David A. Wheeler