evalable6

query

my Promise $p .= new; race for 1..10 { $p.keep }; react { whenever $p { say 'kept' }; whenever Promise.in(5) { done } }

result

(exit code 1) 
A worker in a parallel iteration (hyper or race) initiated here:
  in block <unit> at /tmp/6omjdDwlq8 line 1

Died at:
    Access denied to keep/break this Promise; already vowed
      in block  at /tmp/6omjdDwlq8 line 1