Re: babel default header args as functions

[Tom Gillespie]

I think making the behavior of default arguments consistent with
regular arguments is probably a good thing. I have a number of use
cases that I can imagine would benefit greatly from being able to
define a :header-args: :header (lambda () "yay!") property as a
closure (and actually I assumed that it would just work that way if I
tried to do it, clearly not though). I can't tell for sure if the
patch enables this behavior though or whether I would still get a
Wrong type argument error. I don't see any additional security
implications beyond those already present (or not present) from
allowing closures as arguments to header arguments generally. Looking
at the patch it seems that it preserves the behavior of performing the
evaluation of the closures at the source block, but I'm not 100% sure.
If the default header closures are being evaluated before checking
whether they have been superseded by the headers on a block then that
is incorrect and they should not be evaluated until it is clear that
they are the value of the header for that block and have not been
superseded.
Best!
Tom