Do me a favor, would you? Have a quick look at this code and tell me what you think it does...
MysteryProcedureUsingCodeBlock (long StudentID)!,long ! Declare Procedure FilesOpened BYTE(0) Result long StepNumber long MostAvoidedTeacher cstring(100) CourseTakenQ Queue CourseID long TeacherID long end CourseNotTakenQ Queue CourseID long TeacherID long end CourseQ Queue CourseID long Taken BOOL end TeacherQ Queue TeacherID Long ClassesTaught Long end x long WasTaken bool CODE do OpenFiles STU:StudentID = StudentID get(Student,STU:pkStudentID) if errorcode() do CloseFiles return FALSE end set(Course) loop next(Course) if errorcode() then break. clear(CRSI:Record) CRSI:CourseID = CRS:CourseID set(CRSI:kCourseIDTeacherID,CRSI:kCourseIDTeacherID) WasTaken = false loop next(CourseInstance) if errorcode() or CRSI:CourseID <> CRS:CourseID then break. ENR:StudentID = StudentID ENR:CourseInstanceID = crsi:CourseInstanceID get(Enrollment,ENR:kCourseInstanceUDStudentID) if not errorcode() WasTaken = TRUE break end end if WasTaken clear(CourseTakenQ) CourseTakenQ.CourseID = CRS:CourseID CourseTakenQ.TeacherID = CRSI:TeacherID add(CourseTakenQ) else clear(CourseNotTakenQ) CourseNotTakenQ.CourseID = CRS:CourseID CourseNotTakenQ.TeacherID = CRSI:TeacherID add(CourseNotTakenQ) end end set(Teacher) loop next(Teacher) if errorcode() then break. TeacherQ.TeacherID = TEA:TeacherID add(TeacherQ) end loop x = 1 to records(CourseTakenQ) get(CourseTakenQ,x) TeacherQ.TeacherID = CourseTakenQ.TeacherID get(TeacherQ,TeacherQ.TeacherID) if not errorcode() ! should always find a record TeacherQ.ClassesTaught += 1 put(TeacherQ) end end sort(TeacherQ,-TeacherQ.ClassesTaught) loop while not errorcode() get(TeacherQ,6) delete(TeacherQ) end x = 1 loop get(CourseNotTakenQ,x) if errorcode() then break. TeacherQ.TeacherID = CourseNotTakenQ.TeacherID get(TeacherQ,TeacherQ.TeacherID) if not errorcode() x += 1 else delete(CourseNotTakenQ) end end TeacherQ.TeacherID = CourseNotTakenQ.TeacherID get(TeacherQ,TeacherQ.TeacherID) get(CourseNotTakenQ,random(1,records(CourseNotTakenQ))) do CloseFiles return false ! because this code is not yet complete
How are you making out? Do you have a clear idea of what this code does?
If you study the code long enough you should be able to figure out what it does, but you probably still won't know why it's doing what it does.
Now consider this version of the same code (I've omitted the OpenFiles/CloseFiles routines in both cases):
MysteryProcedureUsingLocalProcedures (long StudentID)!,long ! Declare Procedure map GetStudentRecord(),long BuildListsOfCoursesTakenAndNotTaken(),long CourseWasTaken(),long BuildListOfTeachers(),long CountCoursesTaughtToStudent(),long SortTeacherListByCountOfCoursesTaughtToStudent(),long NarrowTeacherListToFiveMostAvoided(),long NarrowCourseNotTakenListToThoseTaughtByFiveMostAvoidedTeachers(),long CourseIsTaughtByOneOfFiveMostAvoidedTeachers(),long RegisterStudentForRandomlyChosenCourse(),long end FilesOpened BYTE(0) Result long StepNumber long MostAvoidedTeacher cstring(100) CourseTakenQ Queue CourseID long TeacherID long end CourseNotTakenQ Queue CourseID long TeacherID long end CourseQ Queue CourseID long Taken BOOL end TeacherQ Queue TeacherID Long ClassesTaught Long end CODE do OpenFiles StepNumber = 0 Result = Level:Benign Loop while Result = Level:Benign StepNumber += 1 execute StepNumber Result = GetStudentRecord() Result = BuildListsOfCoursesTakenAndNotTaken() Result = BuildListOfTeachers() Result = CountCoursesTaughtToStudent() Result = SortTeacherListByCountOfCoursesTaughtToStudent() Result = NarrowTeacherListToFiveMostAvoided() Result = NarrowCourseNotTakenListToThoseTaughtByFiveMostAvoidedTeachers() Result = RegisterStudentForRandomlyChosenCourse() break end end do CloseFiles Return result GetStudentRecord procedure()!,long code STU:StudentID = StudentID get(Student,STU:pkStudentID) if not errorcode() then return level:benign. return level:notify BuildListsOfCoursesTakenAndNotTaken procedure()!,long code set(Course) loop next(Course) if errorcode() then break. if CourseWasTaken() = Level:Benign clear(CourseTakenQ) CourseTakenQ.CourseID = CRS:CourseID CourseTakenQ.TeacherID = CRSI:TeacherID add(CourseTakenQ) else clear(CourseNotTakenQ) CourseNotTakenQ.CourseID = CRS:CourseID CourseNotTakenQ.TeacherID = CRSI:TeacherID add(CourseNotTakenQ) end end return Level:Benign CourseWasTaken procedure()!,long WasTaken bool code clear(CRSI:Record) CRSI:CourseID = CRS:CourseID set(CRSI:kCourseIDTeacherID,CRSI:kCourseIDTeacherID) loop next(CourseInstance) if errorcode() or CRSI:CourseID <> CRS:CourseID then break. ENR:StudentID = StudentID ENR:CourseInstanceID = crsi:CourseInstanceID get(Enrollment,ENR:kCourseInstanceUDStudentID) if not errorcode() WasTaken = TRUE break end end if WasTaken then return level:benign. return level:notify BuildListOfTeachers procedure()!,long code set(Teacher) loop next(Teacher) if errorcode() then break. TeacherQ.TeacherID = TEA:TeacherID add(TeacherQ) end return Level:Benign CountCoursesTaughtToStudent procedure()!,long x long code loop x = 1 to records(CourseTakenQ) get(CourseTakenQ,x) TeacherQ.TeacherID = CourseTakenQ.TeacherID get(TeacherQ,TeacherQ.TeacherID) if not errorcode() ! should always find a record TeacherQ.ClassesTaught += 1 put(TeacherQ) end end return Level:Benign SortTeacherListByCountOfCoursesTaughtToStudent procedure()!,long code sort(TeacherQ,-TeacherQ.ClassesTaught) return Level:Benign NarrowTeacherListToFiveMostAvoided procedure()!,long x Long code loop while not errorcode() get(TeacherQ,6) delete(TeacherQ) end return Level:Benign NarrowCourseNotTakenListToThoseTaughtByFiveMostAvoidedTeachers procedure()!,long x long code x = 1 loop get(CourseNotTakenQ,x) if errorcode() then break. if CourseIsTaughtByOneOfFiveMostAvoidedTeachers() = Level:Benign x += 1 else delete(CourseNotTakenQ) end end return Level:Benign CourseIsTaughtByOneOfFiveMostAvoidedTeachers procedure()!,long code TeacherQ.TeacherID = CourseNotTakenQ.TeacherID get(TeacherQ,TeacherQ.TeacherID) if not errorcode() then return Level:Benign. return Level:Notify RegisterStudentForRandomlyChosenCourse procedure()!,long code get(CourseNotTakenQ,random(1,records(CourseNotTakenQ))) return Level:Notify ! because this code is not yet complete
I'm pretty confident that you'll find the second version a lot easier to understand, because it breaks up all those blocks of code into procedures with descriptive names.
But the real beauty of this procedure is a construct Mike Hanson recently showed me, and which I've christened the Hanson Loop:
StepNumber = 0 Result = Level:Benign Loop while Result = Level:Benign StepNumber += 1 execute StepNumber Result = GetStudentRecord() Result = BuildListsOfCoursesTakenAndNotTaken() Result = BuildListOfTeachers() Result = CountCoursesTaughtToStudent() Result = SortTeacherListByCountOfCoursesTaughtToStudent() Result = NarrowTeacherListToFiveMostAvoided() Result = NarrowCourseNotTakenListToThoseTaughtByFiveMostAvoidedTeachers() Result = RegisterStudentForRandomlyChosenCourse() break end end do CloseFiles Return result
The Hanson Loop is a while loop - it keeps executing as long as the Result variable is equal to Level:Benign. You could write a siilar loop testing for Result = True, but I think there are some important benefits to using the Clarion return levels, which I'll get to in a moment.
Within the Hanson Loop there's an Execute structure. When the StepNumber variable has a value of 1, the first line in the Execute structure is executed; when the StepNumber variable has a value of 2, the second line executes, and so on.
The very last statement in the Execute structure is simply a break command, which exits the loop.
The beauty of the Hanson Loop is it provides a clear overview of the code being executed by the main procedure, while allowing for clean and efficient error handling.
And this is where the Clarion error levels come in.
The Clarion error levels
I will admit that it has taken me years, almost two decades really, to fully adopt Clarion error levels in my own coding.
The Clarion help has this to say about error levels, in the context of the ABC ErrorManager object:
Six Levels of Treatment
By default, the error manager recognizes six different levels of error severity. The default actions for these levels range from no action for benign errors to halting the program for fatal errors. The error manager also supports the intermediate actions of simply notifying the user, or of notifying the user and letting the user decide whether to continue or abort.
Customizable Treatments
These various levels of treatment are implemented with virtual methods so they are easy to customize. The error manager calls a different virtual method for each severity level, so you can override the default error actions with your own application specific error actions. See the various Take methods for examples.
The recognized severity EQUATEs are declared in EQUATES.CLW. These severity levels and their default actions are:
Level:Benign (0) | no action, returns Level:Benign |
Level:User (1) | displays message, returns Level:Benign or Level:Cancel |
Level:Notify (5) | displays message, returns Level:Benign |
Level:Fatal (3) | displays message, halts the program |
Level:Program (2) | treated as Level:Fatal |
Level:Cancel (4) | used to confirm no action taken by User |
any other value | treated as Level:Program |
You may define your own additional severity levels and their associated actions.