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UPGRADING.md

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This file is part of Logtalk https://logtalk.org/
SPDX-FileCopyrightText: 1998-2024 Paulo Moura pmoura@logtalk.org
SPDX-License-Identifier: Apache-2.0

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

http://www.apache.org/licenses/LICENSE-2.0

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.

UPGRADING GUIDELINES

  • Always check carefully the release notes when updating to a new version, specially, REMOVED, CHANGED, and RENAMED items.

  • Changes in the Logtalk compiler between releases may render some files from older versions incompatible with new ones. You may need to update your local Logtalk user folder by running the logtalk_user_setup shell script.

  • If your Logtalk applications depend on some example files, it is advisable that you check your code against the new version.

  • It's usually a good idea to recompile your source files with the compiler flag clean turned on after upgrading to a new Logtalk release to ensure that all files will be recompiled disregarding any existing intermediate files.

  • In the case of incompatible changes between major Logtalk versions, you may be able to use conditional compilation directives to allow your code to compile and run under multiple versions.

MAJOR LANGUAGE CHANGES FROM LOGTALK 2.x TO LOGTALK 3.x

Structured message printing

The new structured message printing mechanism, an extended implementation of the same mechanism available in some Prolog systems, allows fine-grained control over printing of informative, warning, and error messages. This mechanism is fully customizable using user-defined hook predicates.

Structured question asking

The new structured question asking mechanism complements the structured message printing mechanism and allows fine-grained control over querying the user for data. This mechanism is fully customizable using user-defined hook predicates.

Source file paths

Relative and absolute source file paths are now fully supported by the compiling and loading built-in predicates. In addition, the compiling and loading predicates also accept Prolog source files (with the Prolog code being compiled as Logtalk code).

Removed directives

The synchronized/0 entity directive is no longer supported. But any usage of this directive can be replaced by using instead the synchronized/1 predicate directive.

Removed flags

The following Logtalk 2.x flags are no longer supported in Logtalk 3.x and attempting to use them will result in compiler errors:

  • xmldir, xmldocs, xmlspec, xmlsref, xslfile
  • break_predicate
  • altdirs
  • startup_message
  • smart_compilation
  • misspelt

The XML related flags were removed as generating documenting files is now the responsibility of the lgtdoc tool. The debugger is also no longer a built-in object but a separate tool, debugger. Logtalk 3.x greatly improves support for source file paths, removing the need for the altdirs flag. The flag startup_message is removed due to the introduction of structured message printing in Logtalk 3.x (see also the provided sample settings file). The smart_compilation flag is no longer necessary and the old behavior can now be controlled using the clean flag.

The reload flag, is no longer considered or required for static binding optimizations, which now depend on the optimize flag. In addition, the default value for this flag is now changed, i.e. a file will be reloaded only if changed since last loaded (provided that the any explicit flags are the same as the first time it was loaded).

Deprecated directives, control constructs, and flags

The :/1 control construct is deprecated and only available up to version 3.18.0. Its functionality is now subsumed by the (^^)/1 control construct (aka "super" control construct), which have been generalized to allow calling any imported or inherited predicate. In addition, static binding support for the (^^)/1 control construct have been implemented (enabled by turning on the optimize compiler flag).

The documentation only directives calls/1 and uses/1 are deprecated and only available up to version 3.18.0. The reflection API in Logtalk 3.x now returns all object (and module) dependencies found on sufficiently instantiated (::)/2 and (:)/2 calls when compiling an object or a category.

The alias/3 directive is deprecated and replaced by the new alias/2 directive.

The version flag is deprecated and only available up to version 3.18.0. New code that doesn't require compatibility with Logtalk 2.x should use instead the new version_data flag.

The Logtalk 2.x unknown, singletons, and tmpdir are renamed for clarity to, respectively, unknown_entities, singleton_variables, and scratch_directory. The old names are deprecated and only available up to version 3.18.0.

Stricter syntax

Logtalk 3.x enforces sanctioned syntax for directives. Notably, predicate scope directives and entity relations specified in entity opening directives are restricted to a single argument (which can be, as always, a single item, a list of items, or a comma-separated sequence of items).

Semantic changes

The {}/1 control construct is now opaque to cuts, thus ensuring the same semantics when its argument is known at compile and when it's only known at runtime.

Logtalk and Prolog built-in predicates can no longer be used as messages in order to avoid code portability issues. The workaround is to wrap calls to these predicates using the {}/1 control construct when using them as messages.

Meta-arguments are now always called with the meta-predicate caller full execution context. In addition, when calling a meta-predicate from within a category, meta-arguments are called in the context of the category instead of the context of the object importing the category. This allows moving code that calls meta-predicates between objects and categories without requiring changes.

The initialization/1 directive is only accepted as a source file directive or as an object directive. Usage in protocols and categories is no longer supported as no valid execution context can be defined for the initialization goal.

Reflection support

Logtalk 3.x includes major improvements to reflection support. In particular, it adds entity properties such as calls/2 (for retrieving predicate cross- referencing information) but also removes some subsumed Logtalk 2.x properties such as uses/3 and use_module/3.

Debugging support

The debugger is no longer a built-in pseudo-object. The debugging support have been moved to a Logtalk application, debugger, available in the tools directory. This new tool takes advantage of the improved reflection API.

Documenting support

The compiler no longer outputs XML documenting files for the compiled source files. The documenting support have been moved to a Logtalk application, lgtdoc, available in the tools directory. This new tool takes advantage of the improved reflection API.

New developer tools

A new directory, tools, contains a comprehensive set of developer tools, either new or greatly improved from Logtalk 2.x.