Exception Handling - Revision history

Kasper B H Petersen: /* Introduction to exception handling */

2021-10-13T09:55:32Z

Introduction to exception handling

← Older revision		Revision as of 11:55, 13 October 2021
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	When an exception is continued it consists of the original exception plus some continue information. If it has been continued by several handlers it will contain a lot of continue information in addition to the original exception information. The exception information describes a trace from the point of raise through all the handlers. The <vp>TraceId</vp> variable that is bound in the {{lang2\|Terms\|try-catch\|try-catch}} construction gives access information about the entire trace (hence the name).		When an exception is continued it consists of the original exception plus some continue information. If it has been continued by several handlers it will contain a lot of continue information in addition to the original exception information. The exception information describes a trace from the point of raise through all the handlers. The <vp>TraceId</vp> variable that is bound in the {{lang2\|Terms\|try-catch\|try-catch}} construction gives access information about the entire trace (hence the name).

	As mentioned above the program will terminate with en error message, if an exception is raised and no handler can be found. Therefore programs normally setup an outermost default exception handler. <vp>mainExe::run</vp> setup such a handler in a console program this is the fall-back handler. In a GUI program there is also a default hander in the GUI event loop which will catch exceptions arising from the handling of an event.		As mentioned above the program will terminate with an error message, if an exception is raised and no handler can be found. Therefore programs normally setup an outermost default exception handler. <vp>mainExe::run</vp> setup such a handler in a console program this is the fall-back handler. In a GUI program there is also a default hander in the GUI event loop which will catch exceptions arising from the handling of an event.

	All in all, the lifecycle of an exception is as follows:		All in all, the lifecycle of an exception is as follows:

EJP: Alll, Some times

2016-11-08T16:31:20Z

Alll, Some times

← Older revision		Revision as of 18:31, 8 November 2016
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	...</vip>		...</vip>

	In ~~alll~~ cases the <vp>Exception</vp> is the exception to raise and the rest of the arguments provides additional information about the exception. See also [[Language Reference/Predicates#programPoint\|programPoint in Language Reference]] for information about the programPoint attribute.		In all cases the <vp>Exception</vp> is the exception to raise and the rest of the arguments provides additional information about the exception. See also [[Language Reference/Predicates#programPoint\|programPoint in Language Reference]] for information about the programPoint attribute.

	{{example\|The <vp>cannotCreate</vp> exception from above is raised by the predicate <vp>fileSystem_api::raise_cannotCreate</vp>/<vp>fileSystem_api::raise_cannotCreate_explicit</vp>. The code looks like this:		{{example\|The <vp>cannotCreate</vp> exception from above is raised by the predicate <vp>fileSystem_api::raise_cannotCreate</vp>/<vp>fileSystem_api::raise_cannotCreate_explicit</vp>. The code looks like this:
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	==== Packed Exceptions ====		==== Packed Exceptions ====

	~~Some times~~, e.g., in a client/server application, you catch an exception on the server which you want to handle on the client. In that case you can serialize the exception on the server send it to the client and reraise it as a packed exception.		Sometimes, e.g., in a client/server application, you catch an exception on the server which you want to handle on the client. In that case you can serialize the exception on the server send it to the client and reraise it as a packed exception.

	On the server		On the server

EJP: Typo (I to In)

2016-11-08T16:07:46Z

Typo (I to In)

← Older revision		Revision as of 18:07, 8 November 2016
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	}}		}}

	Many/most programmers will never need to define exceptions, because in many/most cases the exceptions to use are already defined. An exception definition is only needed when the exception must be distinguished from other kinds of exceptions, such that exception handlers can deal specially with that kind of exception. Typically exception definitions are only necessary for exceptions that are raised by library software. I most cases programmers will raise the exception <vp>internal_error</vp>.		Many/most programmers will never need to define exceptions, because in many/most cases the exceptions to use are already defined. An exception definition is only needed when the exception must be distinguished from other kinds of exceptions, such that exception handlers can deal specially with that kind of exception. Typically exception definitions are only necessary for exceptions that are raised by library software. In most cases programmers will raise the exception <vp>internal_error</vp>.

	=== Raising an exception ===		=== Raising an exception ===

Thomas Linder Puls: release

2012-11-24T19:43:57Z

release

← Older revision		Revision as of 21:43, 24 November 2012
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	~~{{Preliminary Documentation}}~~

	An exception is a deviation from the expected. What is an exception in one context may be expected in another context, and thus not an exception in that context.		An exception is a deviation from the expected. What is an exception in one context may be expected in another context, and thus not an exception in that context.

Thomas Linder Puls: /* Catching and handling exceptions */ example/lines

2012-10-25T09:32:58Z

Catching and handling exceptions: example/lines

← Older revision		Revision as of 11:32, 25 October 2012
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	<vip>domains		<vip>domains
	descriptor = descriptor(programPointDescriptor ProgramPoint, exception Exception, kind Kind, namedValue* ExtraInfo, gmtTimeValue GMTTime, unsigned ThreadId).		descriptor = descriptor(programPointDescriptor ProgramPoint, exception Exception,
			kind Kind, namedValue* ExtraInfo, gmtTimeValue GMTTime, unsigned ThreadId).
	</vip>		</vip>

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	if D = exception::tryGetDescriptor(TraceId, fileSystem_api::cannotCreate) then		if D = exception::tryGetDescriptor(TraceId, fileSystem_api::cannotCreate) then
	stdio::write("Cannot write to the file: ", Filename),		stdio::write("Cannot write to the file: ", Filename),
	if string(Description) = exception::tryGetExtraInfo(D, ~~common_exception~~::errorDescription_parameter) then		if string(Description) = exception::tryGetExtraInfo(D, exception::errorDescription_parameter) then
	stdio::writef("; %", Description)		stdio::writef("; %", Description)
	end if,		end if,
	stdio::write("\n")		stdio::write("\n")
	else		else
	~~common_exception~~::continue_unknown(TraceId~~, classInfo, predicate_name()~~, "Filename = ", Filename)		exception::continue_unknown(TraceId, "Filename = ", Filename)
	end if		end if
	end try.</vip>		end try.</vip>

Thomas Linder Puls: /* Raising an exception */ line

2012-10-25T09:28:42Z

Raising an exception: line

← Older revision		Revision as of 11:28, 25 October 2012
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	<vip>clauses		<vip>clauses
	raise_cannotCreate_explicit(ProgramPoint, FileName, LastError) :-		raise_cannotCreate_explicit(ProgramPoint, FileName, LastError) :-
	Desc = ~~exception::~~getLastErrorDescription(LastError),		Desc = getLastErrorDescription(LastError),
	Msg = string::format("Cannot create or open '%%%s'\nError = 0x%08x\n%%%s", ~~fileSystem_exception::fileName_parameter~~, LastError, ~~exception::~~errorDescription_parameter),		Msg = string::format("Cannot create or open '%%%s'\nError = 0x%08x\n%%%s",
	~~exception::~~raise_definiteUser_explicit(ProgramPoint, cannotCreate, Msg,		fileSystem_fileName_parameter, LastError, errorDescription_parameter),
	[namedValue(~~fileSystem_exception::fileName_parameter~~, string(FileName)),		raise_definiteUser_explicit(ProgramPoint, cannotCreate, Msg,
	namedValue(~~fileSystem_exception::path_parameter~~, string(directory::getCurrentDirectory())),		[namedValue(fileSystem_fileName_parameter, string(FileName)),
	namedValue(~~exception::~~errorCode_parameter, unsigned(LastError)),		namedValue(fileSystem_path_parameter, string(directory::getCurrentDirectory())),
	namedValue(~~exception::~~errorDescription_parameter, string(Desc))]).</vip>		namedValue(errorCode_parameter, unsigned(LastError)),
			namedValue(errorDescription_parameter, string(Desc))]).</vip>

	<vp>raise_cannotCreate_explicit</vp> is called with the <vp>ProgramPoint</vp> of the raising predicate, the <vp>FileName</vp> and the windows error code <vp>LastError</vp> that the relevant low level Windows API predicate caused.		<vp>raise_cannotCreate_explicit</vp> is called with the <vp>ProgramPoint</vp> of the raising predicate, the <vp>FileName</vp> and the windows error code <vp>LastError</vp> that the relevant low level Windows API predicate caused.

Thomas Linder Puls: /* Defining an exception */ references

2012-10-22T12:22:09Z

Defining an exception: references

← Older revision		Revision as of 14:22, 22 October 2012
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	…</vip>		…</vip>

	{{Language_Reference/Built-in_entities/Predicates#class_name\|<vp>class_name/0-></vp>}} and {{Language_Reference/Built-in_entities/Predicates#class_name\|<vp>constant_name</vp>}} are built-in predicate that returns the name if the class/constant in which the call occurs. So the line above is equivalent to this:		[[Language_Reference/Built-in_entities/Predicates#class_name\|<vp>class_name/0-></vp>]] and [[Language_Reference/Built-in_entities/Predicates#class_name\|<vp>constant_name/0-></vp>]] are built-in predicate that returns the name if the class/constant in which the call occurs. So the line above is equivalent to this:
	<vip>class fileSystem_api		<vip>class fileSystem_api
	…		…

Thomas Linder Puls: 7.4

2012-05-30T08:27:15Z

7.4

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Thomas Linder Puls: 7.4

2012-05-29T11:32:18Z

7.4

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Kehler: /* Defining an exception */

2010-01-23T11:51:00Z

Defining an exception

← Older revision		Revision as of 13:51, 23 January 2010
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	The implementation looks like this:		The implementation looks like this:
	<vip>~~impement~~ fileSystem_api		<vip>implement fileSystem_api
	…		…
	clauses		clauses