52  Pascal User Manual  program DayTime(Output);  { Program 5.1 - Illustrate enumerated types.  }  type  Days  When  (Mon,  Tue,  Wed,  Thu,  Fri, Sat,  Sun);  (Past,  Present,  Future);  var  Day:  Days;  Yesterday,  Today,  Tomorrow:  Days;  Time: When;  begin  Today := Sun  Pascal can't read a  value of an  emumerated type from Input.  };  Time  := Present;  repeat  case Time of  Present: begin  {Calculate Yesterday}  Time  := Past;  if Today = Mon  then Yesterday := Sun  else Yesterday := pred(Today);  Day  := Yesterday;  Write (Output,  'Yesterday');  end;  Past: begin  {Calculate Tomorrow  Time := Future;  if Today = Sun then Tomorrow := Mon  else Tomorrow := succ(Today);  Day := Tomorrow;  Write (Output,  'Tomorrow');  end;  Future: begin  {Reset to Present  Time := Present;  Day  .- Today;  Write (Output,  'Today');  end;  end;  case Day of  Mon:  Write (Output,  Tue:  Write (Output,  Wed:  Write (Output,  Thu: Write (Output,  Fri: Write (Output,  Sat: Write (Output,  Sun: Write (Output,  end;  'Monday' ) ;  'Tuesday');  , Wednesday' ) ;  , Thursday' ) ;  , Friday') ;  , Saturday') ;  , Sunday' )  Writeln(Output,  Ord(Time)  - 1)  until Time  =  Present  end .  Program 5.1 illustrates some operations on data having an  enumerated type. 