A.7 library(check): Consistency checking

See also

- gxref/0 provides a graphical cross referencer
- PceEmacs performs real time consistency checks while you edit
- library(prolog_xref) implements‘offline’cross-referencing
- library(prolog_codewalk) implements‘online’analysis

This library provides some consistency checks for the loaded Prolog program. The predicate make/0 runs list_undefined/0 to find undefined predicates in‘user’modules.

[det]check

Run all consistency checks defined by checker/2. Checks enabled by default are:

• list_undefined/0 reports undefined predicates
• list_trivial_fails/0 reports calls for which there is no matching clause.
• list_format_errors/0 reports mismatches in format/2,3 templates and the list of arguments.
• list_redefined/0 reports predicates that have a local definition and a global definition. Note that these are not errors.
• list_void_declarations/0 reports on predicates with defined properties, but no clauses.
• list_autoload/0 lists predicates that will be defined at runtime using the autoloader.
• check_predicate_options/0 tests for options passed to predicates such as open/4 that are unknown or are used with an invalid argument.

The checker can be expanded or restricted by modifying the dynamic multifile hook checker/2.

The checker may be used in batch, e.g., for CI workflows by calling SWI-Prolog as below. Note that by using -l to load the program, the program is not started if it used initialization/2 of type main to start the program.

swipl -q --on-warning=status --on-error=status \
      -g check -t halt -l myprogram.pl

[det]list_undefined

[det]list_undefined(+Options)

Report undefined predicates. This predicate finds undefined predicates by decompiling and analyzing the body of all clauses. Options:

module_class(+Classes)

Process modules of the given Classes. The default for classes is [user]. For example, to include the libraries into the examination, use [user,library].

See also

- gxref/0 provides a graphical cross-referencer.
- make/0 calls list_undefined/0

[det]list_autoload

Report predicates that may be auto-loaded. These are predicates that are not defined, but will be loaded on demand if referenced.

See also

autoload/0

To be done

This predicate uses an older mechanism for finding undefined predicates. Should be synchronized with list undefined.

list_redefined

Lists predicates that are defined in the global module user as well as in a normal module; that is, predicates for which the local definition overrules the global default definition.

[det]list_cross_module_calls

List calls from one module to another using Module:Goal where the callee is not defined exported, public or multifile, i.e., where the callee should be considered private.

[det]list_void_declarations

List predicates that have declared attributes, but no clauses.

[det]list_trivial_fails

[det]list_trivial_fails(+Options)

List goals that trivially fail because there is no matching clause. Options:

module_class(+Classes)

Process modules of the given Classes. The default for classes is [user]. For example, to include the libraries into the examination, use [user,library].

[multifile]trivial_fail_goal(:Goal)

Multifile hook that tells list_trivial_fails/0 to accept Goal as valid.

[det]list_strings

[det]list_strings(+Options)

List strings that appear in clauses. This predicate is used to find portability issues for changing the Prolog flag double_quotes from codes to string, creating packed string objects. Warnings may be suppressed using the following multifile hooks:

• string_predicate/1 to stop checking certain predicates
• valid_string_goal/1 to tell the checker that a goal is safe.

See also

Prolog flag double_quotes.

[det]list_rationals

[det]list_rationals(+Options)

List rational numbers that appear in clauses. This predicate is used to find portability issues for changing the Prolog flag rational_syntax to natural, creating rational numbers from <integer>/<nonneg>. Options:

module_class(+Classes)

Determines the modules classes processed. By default only user code is processed. See prolog_program_clause/2.

arithmetic(+Bool)

If true (default false) also warn on rationals appearing in arithmetic expressions.

See also

Prolog flag rational_syntax and prefer_rationals.

[det]list_format_errors

[det]list_format_errors(+Options)

List argument errors for format/2,3.

[multifile]string_predicate(:PredicateIndicator)

Multifile hook to disable list_strings/0 on the given predicate. This is typically used for facts that store strings.

[semidet,multifile]valid_string_goal(+Goal)

Multifile hook that qualifies Goal as valid for list_strings/0. For example, format("Hello world~n") is considered proper use of string constants.

[nondet,multifile]checker(:Goal, +Message:text)

Register code validation routines. Each clause defines a Goal which performs a consistency check executed by check/0. Message is a short description of the check. For example, assuming the my_checks module defines a predicate list_format_mistakes/0:

:- multifile check:checker/2.
check:checker(my_checks:list_format_mistakes,
              "errors with format/2 arguments").

The predicate is dynamic, so you can disable checks with retract/1. For example, to stop reporting redefined predicates:

retract(check:checker(list_redefined,_)).