CP in Haskell through MiniZinc

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BSD3 licensed by Klara Marntirosian, Gert-Jan Bottu, Ruben Pieters


This package was created in the context of the GRACeFUL project.

The haskelzinc library defines an interface to the MiniZinc constraint proramming language. It provides

  • a Haskell abstract syntax tree for the MiniZinc language, with which one can represent MiniZinc models in Haskell
  • a human-friendly DSL for building MiniZinc model representations
  • a pretty printer to print the representation of a MiniZinc model in MiniZinc
  • a parser that returns a representation of the solutions obtained by running the MiniZinc model
  • a set of functions useful for building a custom FlatZinc solutions parser.
  • a set of functions for constructing a model with time and space constraints, including cost related constraints.

An additional module gives the possibility to directly get the solutions of a MiniZinc finite domain model. Option for interactive interface is provided, as well as choice between two solvers: the G12/FD built-in solver of FlatZinc and choco3.


API documentation is provided in hackage. Additionally, a user manual comes together with the installation of the package.


This library is available on hackage. Use cabal install.


  • GHC 7.10.3+ or 8
  • MiniZinc 2.0 or 2.1

Optional requirements

To use choco solver, also required:

  • JDK 8+
  • The following jar files (can be also found in the choco/ directory of the haskelzinc repo)
    • choco_solver (with dependencies) [http://choco-solver.org/Download?q=releases]
    • choco_parser [https://oss.sonatype.org/content/repositories/releases/org/choco-solver/choco-parsers/3.3.3/]
    • ANTLR >4.5.2 java runtime binaries [http://www.antlr.org/download.html]


  1. Create a file HZconf/conf.txt in the same directory level where you want to run your code.
  2. Fill in the corresponding paths by adding the equal sign (=) and the correct path.
    • MINIZINC_DIR: the directory where mzn2fzn and flatzinc executables are located
    • CHOCO_PARSER: the path of the choco parser java library
    • CHOCO_SOLVER: the path of the choco solver java library
    • ANTLR: the path of the antlr java library


MINIZINC_DIR = path/to/dir

Not yet supported

  • MiniZinc enumerated types
  • Set constraints with the choco solver

Running a model

Consider the nineDigitArrangement which can be found in GExamples.hs (root directory). One needs to import module Interfaces.MZinHaskell to use the functions iRunModel or runModel which run a given representation of a MiniZinc model and return its solution(s).


To run the model interactively, use iRunModel and follow the instructions. An example is given below.

> iRunModel nineDigitArrangement
Enter working directory:
Enter model's name: nine
Choose a solver from the list below:
        1. G12/FD
        2. choco3

Integer value associated with the solver: 1
Number of solutions to be returned: 1
Right [[("A",MInt 5),("B",MInt 3),("C",MInt 2),("D",MInt 1),("E",MInt 4),("F",MInt 7),("G",MInt 6),("H",MInt 9),("I",MInt 8),("s",MInt 7448)]]

The script first asks for a working directory. This is where related files will be stored. Next, a name for the model should be given, which will be used for naming the files that will be stored in the working directory. After a name is chosen, the user is presented with a list of supported solvers from which (s)he can choose by entering the corresponding number of the solver. Last, the user is prompted to specify the desired number of solutions. The number of returned solutions will be at most of the user given number. They will be less in case there are no more solutions.


The same functionality can be triggered in a noninteractive manner, with the use of runModel. The user input in iRunModel is entered as arguments (in the same order) of runModel. Make sure to escape special characters in the string of the working directory path. The example below returns the same results as the interactive example above.

runModel nineDigitArrangement "/path/to/desired/directory" "nine" 1 1

- User manual added.
- Addition of two modules that support easy use of time-space constraints, based on the "Geometrical
constraints for CRUD", by N. Beldiceanu, E. Arafailova, R. Douence.
- MiniZinc boolean, integer and floating point literals are now represented easily with
Haskell literals. Functions "int", "bool" and "float" are not necessary any more.
- With the use of the OverloadedStrings option, a MiniZinc variable reference can be
represented easily with the name of that variable as a Haskell string.
- Simpler declaration of variables and user-defined operations.
- Added support for annotations
- Structural changes in the representational system of MiniZinc models
- Module Interfaces.MZAST renamed to Interfaces.MZASTBase
- Module Interfaces.MZAST used for a more human friendly interface for building
representations of MiniZinc models.
- Module Interfaces.MZBuiltIns added. Contains haskelzinc represenatation of predefined MiniZinc
operators, functions, tests, predicates and annotations.
- Module Interfaces.FZSolutionParser provides parsers useful for building custom solutions'
parsers, in case a MiniZinc output item alters the default format of the solutions.
- Compatibility with GHC 8.0.1 tested (and passed)
- Added support for returning specified number of solutions
- Interactive interface of iTestModel improved
- Skips writing .mzn file
- Parses solutions directly, instead of writing into and reading from a file
Depends on 7 packages:
Used by 1 package:
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