FLEX start conditions

Does anybody know how scanner generators like FLEX implement start
conditions? I need to implement start conditions for a simple scanner
generator I wrote a few months ago and the most obvious way I see is to add
a new table that describes for each start condition which states are legal.
However, this is the solution I like least since it's gonna take up an awful
lot of memory. Is there an easier, less memory-consuming way to do it? (I
see how to implement excluding start conditions by building multiple regular
expression trees, but how do I handle the rest of the start conditions?)


      Pascal Schuppli

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