Library /sys$common/syshlp/dbg$help.hlb DEBUG, Language Support, SCAN, Controlling Execution, Breakpoints and Tracepoints  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    You can set breakpoints and tracepoints on procedures, trigger
    macros, syntax macros, and labels, as well as line numbers. For
    example:

    DBG> SET BREAK find_keyword    ! break on a trigger macro
    DBG> CANCEL BREAK exit         ! cancel break on label
    DBG> SET BREAK compare_trees   ! break on a procedure

    Conventional breakpoints and tracepoints are not especially
    convenient for monitoring SCAN's picture matching. Where do you
    set a breakpoint or tracepoint to observe the tokens built by
    your program? There is no statement in your program on which to
    set such a breakpoint.

    To solve this problem, VAX SCAN defines several events. By
    setting breakpoints or tracepoints on these events, you can
    observe the picture matching process.

    The following event keywords are defined for SCAN programs:

    Event
    Keyword        Description

    TOKEN          A token is built.
    PICTURE        An operand in a picture is being matched.
    INPUT          A new line of the input stream is read.
    OUTPUT         A new line of the output stream is written.
    TRIGGER        A trigger macro is starting or terminating.
    SYNTAX         A syntax macro is starting or terminating.
    ERROR          Picture matching error recovery is starting or
                   terminating.

    Use these keywords with the /EVENT qualifier of the following
    commands:

       (SET,CANCEL,ACTIVATE,DEACTIVATE) BREAK
       (SET,CANCEL,ACTIVATE,DEACTIVATE) TRACE

    For example, the following command sets a breakpoint that
    triggers whenever a TOKEN is built:

    DBG> SET BREAK/EVENT=TOKEN

    Recognition of SCAN events is enabled automatically by the
    debugger if the main program is written in SCAN. If you are
    debugging a program written in another language that calls a
    SCAN routine, proceed as follows to set up the SCAN environment:

    1. Enter the SET LANGUAGE SCAN command to enable recognition
       of language-dependent operators, expressions, and other
       constructs (see the SET LANGUAGE command).

    2. Enter the SET EVENT_FACILITY SCAN command to enable
       recognition of SCAN events (see the SET EVENT_FACILITY
       command). The SHOW EVENT_FACILITY command identifies the
       current facility and its events.