1 INQUIRE
  Syntax:   INQUIRE par [prompt] [default]
  where:    par      is the parameter number
            prompt   is the optional prompt
            default  is the optional default value
  Defaults: prompt = 'Give parameter n:'

  Only valid inside macros. If a parameter has not been defined you
  are prompted to give the value of the parameter.  You can force a
  new value for the parameter by giving a negative parameter number. A
  `: ' will automatically be added at the end of the prompt:

  INQUIRE 1 'Give label'
  inq -3

  You can specify a default value for a parameter after the
  prompt. The default is read in as a string. If spaces exist in the
  string you should enclose it in quotes:

  inquire 1 'Give extra offset' 0.5
  inquire 2 'Give title' 'Dummy Title'

  If you do not give the parameter value with the above form the
  default will be taken. If you give a negative parameter number, then
  you will still be prompted for a new value. If you want a parameter
  to take its default value type `=':

  exec test 1 = -3
  test.mnf:
    inquire 1 'Give first value'  2
    inquire 2 'Give second value' 4
    inquire 3 'Give third value'  6
    dep r1 = @1 * @2 * @3
    message 'The result is {ir1,(i6)}'

  would have as answer -12.

  If you are prompted for a parameter and want the default value also
  type `='. Note that no check is made on whether a default value
  exists.
