List matching clauses. What is either a plain specification or a
list of specifications. Plain specifications are:
- Predicate indicator (Name/Arity or Name//Arity)
Lists the indicated predicate. This also outputs relevant
declarations, such as multifile/1 or dynamic/1.
- A Head term. In this case, only clauses whose head
unify with Head are listed. This is illustrated in the
query below that only lists the first clause of append/3.
?- listing(append(, _, _)).
lists:append(, L, L).
- A clause reference as obtained for example from nth_clause/3.
The following options are defined:
- One of
source (default) or
source, for each
clause that is associated to a source location the system tries
to restore the original variable names. This may fail if macro
expansion is not reversible or the term cannot be read due to
different operator declarations. In that case variable names
false), extract the lines from the source
files that produced the clauses, i.e., list the original source
text rather than the decompiled clauses. Each set of contiguous
clauses is preceded by a comment that indicates the file and
line of origin. Clauses that cannot be related to source code
are decompiled where the comment indicates the decompiled state.
This is notably practical for collecting the state of multifile
predicates. For example:
?- listing(file_search_path, [source(true)]).