prolog_codewalk.pl -- Prolog code walker

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 processed:

1. The bodies of all clauses in all user and library modules. This steps collects, but does not scan multifile predicates to avoid duplicate work.
2. All multi-file predicates collected.
3. All goals registered with initialization/1

Options processed:

undefined(+Action)

Action defines what happens if the analysis finds a definitely undefined predicate. One of ignore or error (default is ignore).

autoload(+Boolean)

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.

clauses(+ListOfClauseReferences)

Only process the given clauses. Can be used to find clauses quickly using source(false) and then process only interesting clauses with source information.

module(+Module)

Only process the given module

module_class(+ModuleClassList)

Limit processing to modules of the given classes. See module_property/2 for details on module classes. Default is to scan the classes user and library.

infer_meta_predicates(+BooleanOrAll)

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.

walk_meta_predicates(Boolean)

When false (default true), do not analyse the arguments of meta predicates. Standard Prolog control structures are always analysed.

trace_reference(Callable)

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.

trace_condition(:Cond)

Additional filter condition applied after trace_reference. Called as call(Cond, Callee, Context), where Context is a dict containing the following keys:

caller:Context

Qualified term representing the caller or the atom '<initialization>'.

module:Context

Module being processed

clause:Context

If we are processing a normal clause, the clause reference to this clause.

initialization:Context

If we are processing an initialization/1 directive, a term File:Line representing the location of the declaration.

on_edge(:OnEdge)

If a reference to trace_reference is found, call call(OnEdge, Callee, Caller, Location), where Location is a dict containing a subset of the keys clause, file, character_count, line_count and line_position. If full position information is available all keys are present. If the clause layout is unknown the only the clause, file and line_count are available and the line is the start line of the clause. For a dynamic clause, only the clause is present. If the position is associated to a directive, the clause is missing. If nothing is known the Location is an empty dict.

on_trace(:OnTrace)

As on_edge, but location is not translated and is one of these:

• clause_term_position(+ClauseRef, +TermPos)
• clause(+ClauseRef)
• file_term_position(+Path, +TermPos)
• file(+File, +Line, -1, _)
• a variable (unknown)

Caller is the qualified head of the calling clause or the atom '<initialization>'.

source(+Boolean)

If false (default true), to not try to obtain detailed source information for printed messages.

verbose(+Boolean)

If true (default false), report derived meta-predicates and iterations.

@compat OnTrace was called using Caller-Location in older versions.

 walk_clauses(+Clauses, +OTerm) is det[private]

Walk the given clauses.

 scan_module(+Module, +OTerm) is semidet[private]

True if we must scan Module according to OTerm.

 walk_from_initialization(+OTerm)[private]

Find initialization/1,2 directives and process what they are calling. Skip

bug

- Relies on private '$init_goal'/3 database.

 find_walk_from_module(+Module, +OTerm) is det[private]

Find undefined calls from the bodies of all clauses that belong to Module.

 walk_from_multifile(+OTerm)[private]

Process registered multifile predicates.

 clause_not_from_development(:Head, -Body, ?Ref, +Options) is nondet[private]

Enumerate clauses for a multifile predicate, but omit those from a module that is specifically meant to support development.

 walk_called_by_body(+Body, +Module, +OTerm) is det[private]

Check the Body term when executed in the context of Module. Options:

undefined(+Action)

One of ignore, error

 walk_called_by_body(+Missing, +Body, +Module, +OTerm)[private]

Restart the analysis because the previous analysis provided insufficient information.

 walk_called(+Goal, +Module, +TermPos, +OTerm) is multi[private]

Perform abstract interpretation of Goal, touching all sub-goals that are directly called or immediately reachable through meta-calls. The actual auto-loading is performed by the predicate_property/2 call for meta-predicates.

If Goal is disjunctive, walk_called succeeds with a choice-point. Backtracking analyses the alternative control path(s).

Options:

undecided(+Action)

How to deal with insifficiently instantiated terms in the call-tree. Values are:

ignore

Silently ignore such goals

error

Throw undecided_call

evaluate(+Boolean)

If true (default), evaluate some goals. Notably =/2.

To be done

- Analyse e.g. assert((Head:-Body))?

 trace_condition(:Callee, +TermPos, +OTerm) is semidet[private]

Call call(Condition, Callee, Dict)

 undecided(+Variable, +TermPos, +OTerm)[private]

 evaluate(Goal, Module, OTerm) is nondet[private]

 undefined(:Goal, +TermPos, +OTerm)[private]

The analysis trapped a definitely undefined predicate.

 not_callable(+Goal, +TermPos, +OTerm)[private]

We found a reference to a non-callable term

 print_reference(+Goal, +TermPos, +Why, +OTerm)[private]

Print a reference to Goal, found at TermPos.

Arguments:

Why	- is one of trace or undefined

 register_possible_meta_clause(+ClauseRef) is det[private]

ClausesRef contains as call to a meta-predicate. Remember to analyse this predicate. We only analyse the predicate if it is loaded from a user module. I.e., system and library modules are trusted.

 infer_new_meta_predicates(-MetaSpecs, +OTerm) is det[private]

 calling_metaspec(+Head) is semidet[private]

True if this is a meta-specification that makes a difference to the code walker.

 walk_meta_call(+Index, +GoalHead, +MetaHead, +Module, +ArgPosList, +EndPos, +OTerm)[private]

Walk a call to a meta-predicate. This walks all meta-arguments labeled with an integer, ^ or //.

Arguments:

EndPos

- reflects the end of the term. This is used if the number of arguments in the compiled form exceeds the number of arguments in the term read.

 walk_called_by(+Called:list, +Module, +Goal, +TermPos, +OTerm)[private]

Walk code explicitly mentioned to be called through the hook prolog:called_by/2.

 walk_dcg_body(+Body, +Module, +TermPos, +OTerm)[private]

Walk a DCG body that is meta-called.

 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 same_term, ==, =@= or subsumes_term

 extend(+Goal, +ExtraArgs, +TermPosIn, -TermPosOut, +OTerm)[private]

bug

- :

 variants(+SortedList, -Variants) is det[private]

 predicate_in_module(+Module, ?PI) is nondet[private]

True if PI is a predicate locally defined in Module.

 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.

• module(?Module)
• module_class(+list(Classes))

 translate_location(+Loc, -Dict) is det[private]

 filepos_line(+File, +CharPos, -Line, -Column) is det[private]

Arguments:

CharPos	- is 0-based character offset in the file.
Column	- is the current column, counting tabs as 8 spaces.