JSON input

[dcatteeu]

Hi,

The MiniZinc spec (http://www.minizinc.org/doc-lib/minizinc-spec.pdf) mentions support for input in JSON format (Chapter D).

How do I enable this?

It does not seem to work out of the box. Running

mzn-gecode --all-solutions model.mzn data.dzn

works fine, if data.dzn contains

n = 4;

but not when it contains

{ "n": 4 }

Instead, I get

{"n": 4}
    ^
Error: syntax error, unexpected ':', expecting '}'

model.mzn:

int: n;

var 1..n: x;

solve satisfy;

Versions:

$ mzn-gecode --version
G12 MiniZinc evaluation driver, version 2.1.x
Copyright (C) 2011-2015 The University of Melbourne and NICTA
$ uname -a
Darwin neptune.local 17.2.0 Darwin Kernel Version 17.2.0: Fri Sep 29 18:27:05 PDT 2017; root:xnu-4570.20.62~3/RELEASE_X86_64 x86_64

Any help is much appreciated.

Thanks,

david. 

[Guido Tack]

The data file needs to have the extension .json, the parser currently doesn’t try to auto-detect that format.

Cheers,

Guido

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GUIDO TACK

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[dcatteeu]

Thanks Guido. Seems reasonable to implement it that way.

Unfortunately, I bump into another error:

$ mzn-gecode --all-solutions json-input-test.mzn json-input-test.json

minizinc: more than one model file specified.

minizinc: use --help for more information.

$ cat json-input-test.mzn

int: n;

var 1..n: x;

solve satisfy;

$ cat json-input-test.json

{ "n": 4 }

I see no difference when switching solvers. I tried mzn-chuffed and mzn-g12fd.

Using -D to specify the data on the command line, doesn't help either. Then I get the same syntax error as before.

Do I need to build the latest version myself? 

Thanks,

david.

[guido.tack]

Ah, this is because the minizinc driver executable doesn't recognise json input yet. You have to split up the call into mzn2fzn (for flattening) and fzn-gecode (for solving), piping the output through solns2out, e.g.:

mzn2fzn -Ggecode json-input-test.mzn json-input-test.json

fzn-gecode -a json-input-test.fzn | solns2out json-input-test.ozn

Cheers,

Guido

[dcatteeu]

Great, that works!

[Claudio Cesar de Sa]

Hi Guido

Any improvement about JSON inputs since this thread (2017) or this workaround
Is the scheme to use JSON inputs?

Thanks

CC

[guido.tack]

You can use JSON files (with extension .json) directly with the minizinc driver now. There are still a few limitations (such as array index sets that don't start at 1, and some restrictions around enums) so you may not be able to use JSON with existing models that were written with dzn input in mind, but with any model you write yourself there should be no problem.

Cheers,

Guido

[Claudio Cesar de Sa]

Thanks Guido

It works perfectly. Later I will be sending the code with arrays ...

The test was with a simple code.

Claudio

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[David Wagstaff]

JSON file still has enums issue (as you noted) when using an array of strings in minizinc 3.2.1. 

But the same .mzn and .json work fine in the IDE. I infer that the IDE is simply spawning minizinc on the command line. However, I can't manually get it to work. I can get it to work with a dzn, but the equivalent json is a no go.

[Shuai Wang]

Hi David,

I am using https://github.com/paolodragone/pymzn to parse the json.

On Tue, Dec 10, 2019 at 5:13 PM David Wagstaff <david.w...@gmail.com> wrote:

JSON file still has enums issue (as you noted) when using an array of strings in minizinc 3.2.1. 

But the same .mzn and .json work fine in the IDE. I infer that the IDE is simply spawning minizinc on the command line. However, I can't manually get it to work. I can get it to work with a dzn, but the equivalent json is a no go.

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Thanks,

Shuai Wang, Ph.D.

[guido.tack]

If you send me the files that don't work I can have a look. It really shouldn't behave differently in the IDE. In order for MiniZinc to be able to read enums from JSON files, they need to be encoded into objects rather than passed as lists of strings. For example, value A of an enum type is represented as {"e":"A"} in JSON. This is currently undocumented (but the documentation will be available later today).

Cheers,

Guido