This module walks over the loaded program, searching for callable predicates. It started as part of library(prolog_autoload) and has been turned into a separate module to facilitate operations that require the same reachability analysis, such as finding references to a predicate, finding unreachable code, etc.
For example, the following determins the call graph of the loaded
program. By using
source(true), The exact location of the call in the
source file is passed into _Where.
:- dynamic calls/2. assert_call_graph :- retractall(calls(_, _)), prolog_walk_code([ trace_reference(_), on_trace(assert_edge), source(false) ]), predicate_property(calls(_,_), number_of_clauses(N)), format('Got ~D edges~n', [N]). assert_edge(Callee, Caller, _Where) :- calls(Caller, Callee), !. assert_edge(Callee, Caller, _Where) :- assertz(calls(Caller, Callee)).
- prolog_walk_code(+Options) is det
- Walk over all loaded (user) Prolog code. The following code is
- The bodies of all clauses in all user and library modules. This steps collects, but does not scan multifile predicates to avoid duplicate work.
- All multi-file predicates collected.
- All goals registered with initialization/1
- Action defines what happens if the analysis finds a
definitely undefined predicate. One of
- Try to autoload code while walking. This is enabled by default to obtain as much as possible information about goals and find references from autoloaded libraries.
- Only process the given clauses. Can be used to find clauses
source(false)and then process only interesting clauses with source information.
- Only process the given module
- Limit processing to modules of the given classes. See
module_property/2 for details on module classes. Default
is to scan the classes
- Use infer_meta_predicate/2 on predicates with clauses that
call known meta-predicates. The analysis is restarted until
a fixed point is reached. If
true(default), analysis is only restarted if the inferred meta-predicate contains a callable argument. If
all, it will be restarted until no more new meta-predicates can be found.
- Print all calls to goals that subsume Callable. Goals are represented as Module:Callable (i.e., they are always qualified). See also subsumes_term/2.
- Additional filter condition applied after
trace_reference. Called as
call(Cond, Callee, Context), where Context is a dict containing the following keys:
- Qualified term representing the caller or the atom '<initialization>'.
- Module being processed
- If we are processing a normal clause, the clause reference to this clause.
- If we are processing an initialization/1 directive, a term
File:Linerepresenting the location of the declaration.
- If a reference to
trace_referenceis found, call
call(OnTrace, Callee, Caller, Location), where Location is one of these:
file(+File, +Line, -1, _)
- a variable (unknown)
Caller is the qualified head of the calling clause or the atom '<initialization>'.
true), to not try to obtain detailed source information for printed messages.
false), report derived meta-predicates and iterations.
@compat OnTrace was called using Caller-Location in older versions.
- subterm_pos(+SubTerm, +Term, :Cmp, +TermPosition, -SubTermPos) is nondet
- True when SubTerm is a sub term of Term, compared using Cmp,
TermPosition describes the term layout of Term and SubTermPos
describes the term layout of SubTerm. Cmp is typically one of
- prolog_program_clause(-ClauseRef, +Options) is nondet
- True when ClauseRef is a reference for clause in the program.
Options is a subset of the options processed by
prolog_walk_code/1. The logic for deciding on which clauses to
enumerate is shared with prolog_walk_code/1.