Purpose

#external-exception is a built-in catch name that you can use to catch errors generated by OmniMark's interaction with the outside world. OmniMark will generate a throw to #external-exception when it encounters a problem dealing with the file system, for instance. Many OmniMark external function libraries will also throw to #external-exception when they encounter an error.

If a throw to #external-exception is not caught, OmniMark will generate a throw to #program-error.

#external-exception has three parameters:

• identity, a stream that contains an identifying error code
• message, a stream that contains a description of the error
• location, a stream that contains the location of the error in the OmniMark source code.

When you create a catch for #external-exception, it is only necessary to specify the parameters you will be using in the catch block.

  process
  	local stream my-stream  do
  	open my-stream as file "/just/not/there"
  	catch #external-exception
  		output "Something went wrong. Don't know what it was.%n"
  	done

The following code uses all the parameters of #external-exception.

  process
     local stream my-stream
     open my-stream as file "/just/not/there"
     catch #external-exception
        identity error-code
        message error-message
        location error-location
        output "I know what went wrong:%n"
            || "The error code is: " || error-code || "%n"
            || "The error message is: " || error-message || "%n"
            || "The error location is: " || error-location || "%n"

Related Syntax    #program-error    always    throw    rethrow    catch

Related Concepts    Catch and throw

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