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This file is part of Logtalk
Copyright 2016 Barry Evans and
Paulo Moura

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.


This tool detects likely dead code in Logtalk entities and in Prolog modules compiled as objects. Predicates (and non-terminals) are classified as dead code when (1) there is no scope directive for them and (2) are not called, directly or indirectly, by any predicate with a (local or inherited) scope directive. Predicates (and non-terminals) listed in uses/2 and use_module/2 directives but that are not used are also classified as dead code.

Besides dead code, this tool can also help detect other problems in the code that often result in reporting false positives. For example, typos in alias/2 directives, missing scope directives, and missing meta_non_terminal/1 and meta_predicate/1 directives.

Given the possibility of false positives, care must be taken before deleting reported dead code to ensure that it's, in fact, code that is not used. A common cause of false positives is the use of conditional compilation directives to provide implementations for predicates missing in some systems.

The dead_code_scanner.lgt source file implements the scanning predicates for finding dead code in entities, libraries, and directories. The source file dead_code_scanner_messages.lgt defines the default translations for the messages printed when scanning for dead code. These messages can be intercepted to customize output, e.g. to make it less verbose, or for integration with e.g. GUI IDEs and continuous integration servers.

API documentation

To consult this tool API documentation, open in a web browser the link:


For sample queries, please see the SCRIPT.txt file.


This tool can be loaded using the query:

| ?- logtalk_load(dead_code_scanner(loader)).

Known issues

Use of local meta-calls with goal arguments only known at runtime can result in false positives. When using library or user-defined meta-predicates, it can be helpful to compile the source files with the optimize flag turned on so that the meta-calls may be resolved at compile time and thus allow calling information for the meta-arguments to be recorded, avoiding false positives for predicates that are only meta-called.

Other notes

All source files are formatted using tabs (the recommended setting is a tab width equivalent to 4 spaces).