error: expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `error`
  --> $DIR/main.rs:10:20
   |
LL |     () => { syntax error };
   |                    ^^^^^ expected one of 8 possible tokens
...
LL |     pong!();
   |     ------- in this macro invocation
   |
   = note: this error originates in the macro `pong` (in Nightly builds, run with -Z macro-backtrace for more info)

error: expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `error`
  --> $DIR/main.rs:10:20
   |
LL |     () => { syntax error };
   |                    ^^^^^ expected one of 8 possible tokens
...
LL |     ping!();
   |     ------- in this macro invocation
   |
   = note: this error originates in the macro `pong` which comes from the expansion of the macro `ping` (in Nightly builds, run with -Z macro-backtrace for more info)

error: expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `error`
  --> $DIR/main.rs:10:20
   |
LL |     () => { syntax error };
   |                    ^^^^^ expected one of 8 possible tokens
...
LL |     deep!();
   |     ------- in this macro invocation
   |
   = note: this error originates in the macro `pong` which comes from the expansion of the macro `deep` (in Nightly builds, run with -Z macro-backtrace for more info)

error: aborting due to 3 previous errors