how to do a dynamic parser in X3?

Hi,

So the symbols parser is an example of a dynamic parser in X3.  I am trying to
write a parser for a GIF image file.  A GIF file is a series of chunks.  Chunks
are prefixed with a length indicating the number of bytes in the chunk.  Many
binary formats have the length of a binary block encoded in the stream followed
by <length> bytes (or words or whatever unit) representing the block.

How do we parse this using X3 spirit?

Do we use a success handler for the length to record it in the context and then
somehow use a repeat parser that grabs the repeat count from the context?
What, exactly, does that look like?

I'm hoping to figure this out in time for a presentation on X3 to Utah C++
Programmers on Sept. 13th.

Thanks,

-- Richard
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