VFILT()         Interactively build a filter

Description:
  VFILT() provides a non-screen destructive user interface to allow the
  user to select a list of fields, logical connectives and comparison
  constants from pop-up light bar windows.


Syntax:     
  VFILT()


Pass:       
  Nothing


Return:     
  <expC>   = Desired filter (blank if the user specified "no filter")


Notes:      


Example:    
  c_Filter = VFILT()
  IF EMPTY(c_Filter)
     c_Filter = ".T."
  ENDIF
  DO WHILE &c_Filter
     .
     .
     .
     SKIP
  ENDDO


Usage:      
  VFILT() is designed to provide the uninitiated user with an easy
  interface to "filter" specification building.  It is database
  independent and limits the choices available in the light bar menus to
  those that are applicable to the variable type selected.  As the user
  selects fields, relational operators and comparison constants, the
  string VFILT() builds is also displayed on the screen.

  VFILT() alone is not a powerful function, but when combined with the
  macro substitution capabilities of Clipper, the two become very
  powerful indeed.  The string returned by VFILT() is suitable for macto
  subsitution in the SET FILTER TO command as well as any FOR clause in
  any Clipper command supporting that clause (such as REPORT, SORT,
  COPY, LIST, DO WHILE, etc.)