fail). The atom
allrefers to all ports. If the port is preceded by a
sign, the trace point is cleared for the port. If it is preceded by a
, the trace point is set.
The predicate trace/2 activates debug mode (see debug/0). Each time a port (of the 4-port model) is passed that has a trace point set, the goal is printed as with trace/0. Unlike trace/0, however, the execution is continued without asking for further information. Examples:
|Trace all ports of hello with any arity in any module.|
|Trace failures of foo/2 in any module.|
|Stop tracing bar/1.|
The predicate debugging/0 shows all currently defined trace points.