OmniMark has the capability to run processes as co-routines. Co-routines occurs whenever a program is generating markup which is then fed to the XML or SGML parser. This occurs in up-translate and context-translate programs, in programs that do subdocument processing, and in programs that use an string source function to supply input to the parser in a do xml-parse and do sgml-parse.

The use of co-routines has three principal advantages:

• It eliminates the need to buffer generated markup before processing it with the parser.
• It allows the parser to report errors in generated markup as that markup is generated, allowing you to use the parser to simplify error detection and correction in programs that generate markup.
• It allows you to use the current state of the parse tree (as expressed in the execution state of the markup rules) to guide markup generation, allowing you to do context-sensitive markup building.

For the most part, you do not need to concern yourself with the mechanics of co-routines. OmniMark handles all the details for you. However, there are some important restrictions you need to be aware of:

• Each co-routine has its own groups.
• save and save-clear operations are specific to the co-routine in which they occur.
• A co-routine that is supplying input to the parser cannot itself invoke the parser. Thus you cannot use do xml-parse and do sgml-parse in an string source function or in the find rules of an up-translate or context-translate program (unless those rules are processing the results of a submit action initiated in a markup rule, and therefore acting on the output of the parser rather than the input).
• Stream variables belong to the co-routine that opened them. If you want one co-routine to be able to write to a stream opened by another co-routine, you need to open that stream with the domain-free modifier. Note that it may not always be obvious which co-routine a certain piece of code is running in. For instance, a find rule that could be fired either by the main input of a cross-translate or up-translate program, or by input from a submit action in a markup rule would be in one co-routine in the first instance and in another co-routine in the second instance.
• using nested-referents can only be used in one co-routine at a time.

If you write code that depends on the interaction between two co-routines, you may need to be aware of the rules OmniMark uses when switching from one co-routine to another.

• In general, OmniMark switches co-routines at its own discretion. You cannot control the switch, but you may be able to write a test in one routine to see where the other routine is up to. For instance, in the scanning routine, you can test to determine what the current element is in the parsing routine using the element is test.
• There is guaranteed to be a context switch at the end of an output statement in the scanning routine, except as follows.
• There is guaranteed not to be a context switch in the scanning routine for the duration of a repeat over loop or a using block applied to the attributes shelf, the data-attributes shelf, or a list-valued attributes shelf.

Related Syntax    do sgml-parse

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