[bug-recutils] New %constraint special field and => operator

[Jose E. Marchesi]

Hi folks.

I just pushed a patch providing support (implementation, tests and
documentation) for two new facilities:

- A new sex operator => (implies) with semantics:

    A => B means !A || (A && B)

  Usage example: if the task is closed then it must have at least one
  ClosedBy field:

    Status = 'CLOSED' => #ClosedBy

- A new special field %constraint, which adds a sex-driven constraint to
  the records of that type.  Example:

  %rec: Task
  %type: Start,End date
  %constraint: Start << End
  %constraint: Status = 'CLOSED' => #End

  Meaning that for any task the Start date cannot be after the Start
  date (which makes sense :D) and that if a class is closed then it must
  have an End date.

As always testing, comments and patches are welcome :)

PS: Is %constraint the better name for this special field?

-- 
Jose E. Marchesi         http://www.jemarch.net
GNU Project              http://www.gnu.org