Access "current duration" from music functions

[Lukas-Fabian Moser]

Folks,

the following question came up (well, by me) in the recent thread start 
by Urs Liska "Combine Text/Lyrics with bass figures":

The LilyPond parser (?) has some notion of "current duration": A note 
with explicit duration sets the next duration that is assumed if none is 
given. Hence { a4 b a b8 a b } will create three crotchets followed by 
three quavers.

Is it possible to access this "current duration" from a music or scheme 
function?

a) for reading: in order to create events with the same duration that 
any note would get if directly entered?
(This is possible by using #{ $pitch #} and the like, but that does not 
make the duration in itself scheme-readable.)

Something like { a8. \myFunction c16 } where \myFunction, for instance, 
displays "I would create a 8."

b) for writing: in order to tell the parser which duration to assume for 
the next explicitly entered note (if it does not have an explicit 
duration) ?

Something like { a4 \myGunction b a } where \myGunction performs some 
magic such that the following b a are interpreted as b8 a8?

Best
Lukas