Rule SelectRuleByParam
  output 'message.txt'
  param $NAME := "A"
Flow
    case $NAME
  when "A"
  rule A
  when "B"
  rule B
  when "C"
  rule C
  end

End

Rule A
  output 'message.txt'
Action
  echo "This is rule A." > {$O[1]}
End

Rule B
  output 'message.txt'
Action
  echo "This is rule B." > {$O[1]}
End

Rule C
  output 'message.txt'
Action
  echo "This is rule C." > {$O[1]}
End