The FlatZinc interpreter described here is based on “Specification of FlatZinc, version 1.6”, available at http://www.minizinc.org/specifications.html.
A FlatZinc program can be run directly using
fzn_run_file/[1,2] and fzn_run_stream/[1,2], as well as
with spfz, a simple command-line tool interface to
fzn_run_file/[1,2] (for details, see too-spfz). For
example, a program for solving the 4 Queens problem, located in
library('zinc/examples/queen4.fzn'), can be run by the following
goal:
| ?- fzn_run_file(library('zinc/examples/queen4')).
or command:
% spfz $SP_LIBRARY_DIR/zinc/examples/queen4
The following solution is then written on the current output stream:
q = array1d(1..4, [2, 4, 1, 3]);
----------
Note the ten consecutive dashes after the solution.
The following goal can be used to find all solutions:
| ?- fzn_run_file(library('zinc/examples/queen4'), [solutions(all)]).
or command:
% spfz $SP_LIBRARY_DIR/zinc/examples/queen4 -a
The following solutions are then written on the current output stream:
q = array1d(1..4, [2, 4, 1, 3]);
----------
q = array1d(1..4, [3, 1, 4, 2]);
----------
==========
Note the ten consecutive equal signs after all solutions have been found.
FlatZinc programs are not intended to be written (or read) by humans,
but rather to be automatically generated. One way to generate a FlatZinc
program is by using a MiniZinc-to-FlatZinc translator, such as
mzn2fzn, provided by the G12 project. One use of this
translator is to first generate a FlatZinc program from a MiniZinc
program, e.g. by the following command line (queen.mzn and
queen4.dat can be found in library('zinc/examples')):
mzn2fzn -G sicstus --data queen4.dat --output-to-file queen4.fzn queen.mzn
The resulting FlatZinc program queen4.fzn can then be run as
described above. If a generated FlatZinc program is not desired, another
use of mzn2fzn is to pipe its result directly to a SICStus
process, e.g. by the following command:
mzn2fzn -G sicstus --data queen4.dat --output-to-stdout queen.mzn | sicstus --goal 'use_module(library(zinc)), fzn_run_stream(user_input), halt.'
or, simpler:
minizinc -G sicstus --data queen4.dat queen.mzn -f spfz
or, even simpler:
minizinc -G sicstus -D n=4 queen.mzn -f spfz
or, simpler still:
mzn-sicstus -D n=4 queen.mzn
Please note: The translator mzn2fzn needs to be made
aware of the SICStus specific global constraint definitions, located in
library('zinc/globals'). This is necessary in order for the
MiniZinc-to-FlatZinc translation to be SICStus specific. If this
is not done, the SICStus interpreter may run the resulting FlatZinc
program significantly slower. In the commands given above, this is done
by the option -G sicstus, which requires that there be a
symbolic link /opt/minizinc-1.6/lib/minizinc/sicstus pointing at
library('zinc/globals'). If you are unable to add such a link,
an alternative to -G sicstus is to pass the path to
library('zinc/globals') in the --search-dir option of
mzn2fzn.
It is also possible to just load a FlatZinc program into SICStus by
fzn_load_file/2 and fzn_load_stream/2. The loaded FlatZinc
program can then be processed further from within SICStus, e.g. by
retrieving some FlatZinc variables using fzn_identifier/3 and
posting additional library(clpfd) constraints or applying a
Prolog labeling predicate on those variables.
Finally, it is also possible to load and run MiniZinc programs directly from within SICStus by using the predicates described in MiniZinc. These predicates all rely on the availability of an external MiniZinc-to-FlatZinc translator such as mzn2fzn, as well as an external solution printer such as solns2out (see MiniZinc).