Callbacks in the abstact data types and extra contextual data

[Marc Nieper-Wißkirchen]

Hi,

a number of modules (like the hash module or the list module) allow
the user to specify callbacks (e.g. a comparison function).
Unfortunately, these procedures do not take a context parameter, which
can be a problem because C lacks closures.

The original qsort function in stdlib.h has the same problem. Glibs
has remedied the problem by introducing qsort_r.

It would be nice if the modules hash, list, xlist, oset, xoset, ...
are extended in a similar way. We would essentially need new
constructors, say with the '_r' suffix.

Marc