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This file is part of Logtalk https://logtalk.org/ SPDX-FileCopyrightText: 1998-2023 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.

This directory contains sample scripts for selected backend Prolog compilers for embedding Logtalk and Logtalk applications. See the SCRIPT.txt file for usage examples.

These scripts allow pre-compilation of the Logtalk compiler/runtime and optionally of a Logtalk application. This is a common requirement for embedding, specially when deploying applications in read-only file systems. These sample scripts should be regarded as starting points as actual use often requires customization (e.g., the starting goal, inclusion of a top-level interpreter, etc).

An alternative, available in some backend Prolog compilers such as SICStus Prolog, SWI-Prolog, and YAP, is to create a saved state after loading Logtalk and a Logtalk application (or the generated Prolog code for Logtalk and a Logtalk application). Saved states are usually executable files that embed both a Prolog runtime and application code. See the SCRIPT.txt file for some examples. For details on creating and using saved states, see your backend Prolog compiler documentation.

Note that the provided scripts don't handle applications composed of both Logtalk and Prolog source files. In these cases, either move (if possible) the Prolog code into Logtalk source files or customize the embedding scripts to include the contents of the Prolog files into the generated embedding files.

Running the embedding scripts

On POSIX systems, the scripts require the Bash shell.

On Windows, experimental PowerShell scripts are available for selected backends. Using the PowerShell scripts may require first changing the execution policy:

PowerShell.exe -ExecutionPolicy Unrestricted

In alternative, a possible solution to run the Bash shell scripts is to install either the Windows Subsystem for Linux (WSL) or Git for Windows. Both provide access to a Bash shell. In both cases, use full paths with forward slashes (e.g., `C:/Users/jdoe/collect`) and without environment variables. You must also specify the temporary directory for intermediate files using the scripts -t option. Also, symbolic links may not work and use of actual paths to files may be required.

Settings for embedded applications

The scripts accept a command-line option for specifying a settings file. See the settings-embedding-sample.lgt file for settings suggestions for embedding applications. Notably, the reload flag should usually be set to skip to prevent reloading of already loaded code when running the embedded application or saved state. You may also want to turn off the source_data flag to reduce the size of your application. When a settings file is passed as argument to the embedding scripts, the backend adapter file ia automatically patched, changing the value of the settings_file flag to deny, to prevent using any settings file accessible on a computer where the embedded application is run to disturb it.

It's also possible to not include any settings file by using the `-s none` option. This is mostly useful when generating a new top-level executable that only includes the Logtalk compiler/runtime.

Library paths for embedded applications

The scripts also accept a command-line option for specifying a paths file. This paths file must provide definitions for the logtalk_library_path/2 predicate for all libraries loaded by the application being embedded. The following query can be used to find the names of all the libraries used by a loaded application:

| ?- setof(Library, File^(logtalk::loaded_file_property(File, library(Library))), Libraries).

To help ensure that the embedded application is relocatable, load it and verify that the following query fails:

| ?- setof(Library, File^(logtalk::loaded_file_property(File, library(Library))), Libraries), member(Missing, Libraries), \+ logtalk_library_path(Missing, _).

Avoiding dependencies on the Logtalk environment variables

To avoid dependencies on the Logtalk LOGTALKHOME and LOGTALKUSER environment variables, the sample scripts support an option for expanding library aliases paths in the paths and settings files. This option also allows (in general) the safe inclusion of the application loader files. If for some reason this option is not desirable, the embedded application or saved state should be run in a process that sets (possibly just for itself) the LOGTALKHOME and LOGTALKUSER environment variables to the values used during the pre-compilation of the Logtalk resources. For example, in a POSIX system, you can use something like:

$ LOGTALKHOME=/usr/local/share/logtalk LOGTALKUSER=/home/user/logtalk ./saved_state

Known issues

The Bash version of the embedding scripts use GNU sed when available. Notably on macOS, if you get sed errors when running the embedding scripts, try installing GNU sed (using e.g. Homebrew or MacPorts).