Deal with MiniZinc files

You can find here the instructions to parse and solve MiniZinc files with Choco-solver. The first thing to understand is that MiniZinc is a high-level constraint modeling language and choco-solver is not able to parse MiniZinc files directly. Actually, MiniZinc files must be converted into FlatZinc files before being parsed by Choco-solver.

There exists different ways to parse and solve MiniZinc files with Choco-solver. The recommended way is to use the MiniZinc IDE, which is a graphical user interface that allows to write, parse and solve MiniZinc files.

Pre-requisites

Before starting, you need to download the Choco-solver jar file that contains the parser for FlatZinc files. This jar file is available on the Choco-solver repository on GitHub. Or you can build it from the source code. In that case, you need to get the jar file from the parsers/target directory. Select the jar file that contains the -light suffix.

Executable script

To parse and solve FlatZinc files, you need an executable script that calls the Choco-solver parser. This script is available in the parsers/src/main/minizinc directory of the Choco-solver repository on GitHub. The entry point of this script is the fzn-choco.py file, which is a Python3 script that calls the Choco-solver parser. Unfortunately, MiniZinc requires an executable script, so you need to create a shell script that calls the Python script.

That’s why two additional files are provided:

• a bash shell script for Linux and maxOS systems, named fzn-choco.sh
• a batch file script for Windows systems, named fzn-choco.bat to call the Python3 script from the MiniZincIDE.

MiniZinc IDE

Now, Choco-solver can be added as a third-Party Solver in MiniZinc IDE in MiniZincIDE. This step requires to create a solver configuration file (with .msc extension) that contains some basic information. With respect to MiniZinc specification, this file can be added in:

the directory $HOME/.minizinc/solvers on Linux and macOS systems, and the Application Data directory on Windows systems.

Important

Before moving the file to the correct directory, it must be edited to set the correct paths. There are two fields in the .msc file that must be set:

• "mznlib": the absolute path to the directory containing the global constraints definition, i.e. mzn_lib directory.
• "executable": the absolute path to the executable script fzn_choco.sh or fzn-choco.bat depending on your OS.

The script referred to in this file (choco.msc), together with global constraints definition can be downloaded from the MiniZinc repository on GitHub.

1. Edit choco.msc to set the "mznlib" and "executable" fields.
   1. The "executable" field should be set to the path of the executable script fzn-choco. You must set the full path to the script, including the extension (like .exe or .bin).
   2. The "mznlib" field should be set to the absolute path of the directory containing the global constraints definition, i.e. mzn_lib directory.
2. Copy choco.msc to the directory recommended by MiniZinc (please refer to the MiniZinc documentation).
3. Restart MiniZinc IDE.

Dockerfile

Note that the fzn-choco script can be used in a Docker container. A Dockerfile is available in the parsers/src/main/minizinc directory of the Choco-solver repository on GitHub. Some Choco-solver Docker images for the MiniZinc Challenge are available on hub.docker.com/.