How to use --define:SYMBOL:VAL option?

[yuutayamada]

I compiled following content with: nim c -r --define:line:10 foo.nim but I got: 
foo.nim(2.9) Error: undeclared identifier: 'line'

How can I access the line variable? or Am I doing something wrong?
    
    
    when defined(line):
      echo line
    

Thanks