Andreas Ulbrich <andreas.ulbrich@matheversum.de> writes:
> In the documentation I can't find, that / is not possible as an unary
> operator.
> Are there any restrictions.
Yeah, if you look in the bison grammar you'll find out that the operators
with special precedence are hard-wired as to which syntaxes are allowed:
+ - prefix or infix
* / % ^ < > = infix only
It's possible that if we just added some more productions these could be
used in nonstandard ways. But I think interest in that is really pretty
low, and it might lead to behavior that would be surprising to people
who aren't interested in using them in weird ways.
regards, tom lane