error: 1 positional argument in format string, but no arguments were given
  --> $DIR/main.rs:6:5
   |
LL |     myprintln!("{}");
   |     ^^^^^^^^^^^^^^^^
   |
   = note: this error originates in the macro `concat` which comes from the expansion of the macro `myprintln` (in Nightly builds, run with -Z macro-backtrace for more info)

error: aborting due to previous error