[asdf-devel] Backward incompatible improvements

Faré fahree at gmail.com
Sun Mar 30 02:00:28 UTC 2014

> I haven't checked recently, but in the past ASDF files have had significant
> code even before the system definition.  It was common to find conditionals
> based on *features*, comments for users to select from a few customization
> options, numbers being read, etc.
> Once you have read the form, it is too late to modify the environment that
> is used to read it.  Thus I suggested that we adopt a convention to check
> for a "magic header" that changes the syntax used for the rest of the file.
> The suggested syntax was meant to make this header invisible to legacy
> systems, unambiguous in meaning, extensible, and fairly easy to parse for
> new sysetms.
Emacs already has two such conventions.
If someone wants to implement such a thing, that's the way to go.
I'm sure Robert accepts patches, though in this case,
you might want to start with an ASDF extension,
a la asdf-encodings, that does exactly that with respect to encodings
(many thanks to Douglas Crosher).

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