I asked because I couldn't think if a way to do it and it seems generally useful to be able to use interesting values of undef (eg. Perl6 is to support this for exceptions and potentially other things).

I can solve the problem at hand by other means, so my question is not seeking a specific solution but a general technique, and knowledge about what is possible in Perl 5.

Since you are curious about the context, I have an application which uses Storable for persistence and undef is used to represent "no answer". This works nicely for the core engine. I'm now working on a tool chain to convert a this data into various presentation formats, a few of which would like to distinguish between existant/nonexistant undefs and present them differently (the distinction being "no answer"/"no answer, never saw the question"). The distinction is more in the minds of the users than anywhere else, most of the utilities will not make this distinction and shouldn't be troubled by it. My current solution is to maintain the flags in a separate structure in parallel to the main data stream.

My original question mentioned YAML because the data stream pipeline uses IO::YAML pass data beween utilities.

If you have other suggestions, they're welcome,

Brad

In reply to Re^2: Special undefs with attributes by bsb
in thread Special undefs with attributes by bsb

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