This library prints accesses to specified predicates by wrapping the predicate.
- trace(:Pred) is det
- trace(:Pred, +PortSpec) is det
- Print passes through ports of specified predicates. Pred is a,
possible partial, specification of a predicate as it is also used be
spy/1 and similar predicates. Where a full predicate specification
is of the shape
Module:Name/Arity(or `//Arity for non-terminals), both the module and arity may be omitted in which case Pred refers to all matching predicates. PortSpec is either a single port (
redo), preceded with
-or a list of these. The predicate modifies the current trace specification and then installs a suitable wrapper for the predicate using wrap_predicate/4. For example:
?- trace(append). % lists:append/2: [all] % lists:append/3: [all] % append/1: [all] true. ?- append([a,b], [c], L). T  Call: lists:append([a, b], [c], _18032) T  Call: lists:append([b], [c], _19410) T  Call: lists:append(, [c], _20400) T [28 +0.1ms] Exit: lists:append(, [c], [c]) T [19 +0.2ms] Exit: lists:append([b], [c], [b, c]) T [10 +0.5ms] Exit: lists:append([a, b], [c], [a, b, c]) L = [a, b, c]. ?- trace(append, -all). % lists:append/2: Not tracing % lists:append/3: Not tracing % append/1: Not tracing
The text between  indicates the call depth (first number) and for all ports except the
callport the wall time since the start (call port) in milliseconds. Note that the instrumentation and print time is included in the time. In the example above the actual time is about 0.00001ms on todays hardware.
- tracing(:Spec, -Ports)
- True if Spec is traced using Ports
- notraceall is det
- Remove all trace points
The following predicates are exported, but not or incorrectly documented.