@Kha Note that I had to write the weird pattern
```
match_syntax stx with
| `(notation:$prec $items* => $rhs) => expandNotationAux stx prec items rhs
| `(notation $noprec* $items* => $rhs) => expandNotationAux stx none items rhs
| _ => Macro.throwUnsupported
```
with the weird `$noprec*` to match the case where the optional
precedence is not provided. I realized this is not a bug, but
I guess most users will be puzzled by this behavior. If we had a kind
for `notationItem`, I would be able to write
```
`(notation $items:notationItems* => $rhs)
```
@Kha I implemented the solution 1 I described at Zulip.
I also tried to document the issue, and made sure test
`choiceMacroRules` fail if the bug is reintroduced.
@Kha Could you please double check these modifications.
I added a no-op for `checkRbpLt`. It is used at the `Sort` and `Type`
parsers.
As I described in previous commits, the `checkRBPGreater` comment and
implementation were misleading. It was actually succeeding when the
rbp was less than or equal to the given parameter. So, it was renamed
to `checkRbpLe`. So, is the depArrow parenthesizer ok? I did not check.
I updated the PPRoundtrip.lean.expected.out to make sure the tests
succeed, but we should revise it if there is a problem with the
modifications at Parenthesizer.lean
@Kha It is not clear to me why I had to change the following line
```
-syntax term ">>>" term : foo
+syntax term:1 ">>>":1 term : foo
```
The test breaks without it.
@Kha
I was having several errors of the form
```
224: /Users/leonardodemoura/projects/lean4/build/release/stage0.5/bin/../include/lean/runtime/exception.h:23:13: error: exception specification of overriding function is more lax than base version
224: virtual ~throwable() noexcept;
224: ^
224: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/exception:102:13: note: overridden virtual function is here
224: virtual ~exception() _NOEXCEPT;
224: ^
224: In file included from myfuns.cpp:1:
```
As far as I can tell, the error ocurrs because my compiler uses an old
C++ standard if the option `-std` is not used.
I guess `-std=c++11` would also works, but I decided to use the same
standard we used to compile Lean.
Since we don't use static initializers, really the only difference between using `clang` and `clang++` is the default
inclusion of the C++ standard library.
