Range syntax

[Michael Meissner]

| Uwe Hollerbach (uhaacm.princeton.edu) suggested to me the use of
| -- as a range delimiter.  For example, `int {a -- b}' or
| `case a -- b:'.
| 
| This syntax looks natural for a range and ought to be unambiguous
| in all contexts.

I would be real careful about using --, since I can imagine that it
would cause most parsers headaches, since a lot of compilers typically
don't have completely separate rules for expressions and constant
expressions.