> I'm trying to trace a function, but I get always: "trace -- Undefined".
> Is there any required lib (.l) to trace?
Yes and no.
You need to be in debug mode, for which the recommended way is to put a
single '+' argument at the end of the command line:
$ pil +
This causes debug mode to be switched on upon interpreter startup, and
also loads "@lib/debug.l" in an early stage (before evaluating command