main = do print 'b'
          args <- getArgs
          let isB = head args
          when (isB /= "isB") (error "B is not B!")
main = do print 'b'
          args <- getArgs
          let isB = head args
          when (isB /= "isB") (error "B is not B!")
main = do print 'b'
          args <- getArgs
          let isB = head args
          when (isB /= "isB") (error "B is not B!")