exercise: Phone
version: 4
plan: 12
tests: |-
  for @($c-data<cases>[0]<cases>) {
    if .<expected> {
      is clean-number(.<phrase>), |.<expected description>;
    } else {
      nok clean-number(.<phrase>), .<description>;
    }
  }

unit: module
example: |-
  sub clean-number ($number is copy) is export {
    $number ~~ s:g/<:!Nd>//;
    $number ~~ /^ 1? ( [ <[2..9]> <:Nd> ** 2 ] ** 2 <:Nd> ** 4 ) $/ ?? ~$0 !! Nil;
  }
stub: |-
  sub clean-number ($number) is export {
  }