GENVAL()

  Short:
  ------
  GENVAL() Generic VALID clause validation with message

  Returns:
  --------
  <lValid> => logical result of passed condition

  Syntax:
  -------
  GENVAL(expValid,expMessage)

  Description:
  ------------
  Evaluates <expValid>, which is either a bode block or
  a string to be macro expanded, as a logical value. If result is
  False, displays message <expMessage> and waits for a keypress.
  <expMessage> can be a single string, or an array of strings (see
  aMsg() ).

  Examples:
  ---------
   if genval("fcount() < 60",'Too many fields')
       COPY TO TEMP
   endif

   * ...or as a VALID CLAUSE macro'd

   @10,10 get lname VALID ;
     GENVAL("!empty(lname)","Need a last name")

   * ...or as a VALID CLAUSE eval'd

   @10,10 get fname VALID ;
     GENVAL( { || !empty(fname) },"Need a last name")

  Source:
  -------
  S_GENVA.PRG