Add tracing option
Implement "trace mode", i.e., show every function call to be evaluated and, if possible,
also the result (HNF) of the call. Compare the PAKCS option :set +debug
and the possibilities
offered by this mode. This could be implemented by a modified run-time system so that the
standard run-time system is not influenced by this additional mode.
Try to implement this first in a new experimental branch.
Similarly to showing failures in case of run-time errors, one could also offer to show the current function call or the complete expression.