Failed to create instance

[Sirneij]

I have this directory:

.
├── facts
│   └── edge.facts
├── test.cpp
├── test_souffle.dl

The contents of which are:

facts/edge.facts

1	2
1	3
1	4
1	5
1	6
1	7
1	8
1	9

test.cpp

#include <souffle/SouffleInterface.h>
#include <iostream>
#include <string>

int main(int argc, char *argv[])
{
    using namespace std::chrono;

    if (argc < 3)
    {
        std::cerr << "Usage: " << argv[0] << " <datalog_file> <facts_file>" << std::endl;
        return 1;
    }

    const std::string datalogFile = argv[1];
    std::cout << "Datalog file: " << datalogFile << std::endl;
    const std::string factsFile = argv[2];
    std::cout << "Facts file: " << factsFile << std::endl;

    // Initialize Souffle program
    souffle::SouffleProgram *prog = souffle::ProgramFactory::newInstance(datalogFile);
    if (prog == nullptr)
    {
        std::cerr << "Could not create Souffle program instance." << std::endl;
        return 1;
    }

    // Load facts from file
    prog->loadAll(factsFile);

    // Run the program
    prog->run();

    // Retrieve relation "path" which contains the results of transitive closure
    souffle::Relation *path = prog->getRelation("path");
    if (path == nullptr)
    {
        std::cerr << "Relation 'path' not found." << std::endl;
        return 1;
    }

    // Iterate over the tuples in the relation
    for (auto &tuple : *path)
    {
        int start, end;
        tuple >> start >> end;
        std::cout << "Path: " << start << " -> " << end << std::endl;
    }

    // Cleanup
    delete prog;
    return 0;
}

test_souffle.dl

.decl edge(x: number, y: number)
.input edge

.decl path(x: number, y: number)
.output path
path(x, y) :- edge(x, y).
path(x, y) :- path(x, z), edge(z, y).

When I issue the following command in my terminal:

souffle-compile.py test.cpp -o souffle_tmp

souffle-compile.py was installed alongside the souffle installation. I had used it to compile .cpp files generated by souffle before now without issues.

It compiles and souffle_tmp gets generated. However, when I want to run it:

./souffle_tmp ./test_souffle.dl ./facts/edge.facts

or

./souffle_tmp test_souffle.dl facts/edge.facts

I get this error:

Datalog file: test_souffle.dl
Facts file: facts/edge.facts


Could not create Souffle program instance.

What I can think of is that the souffle instance could not be created. Is something wrong with my code or something?

[quentin]

Hi,
newInstance does not take a datalog file name, it takes the name of a soufflé program (look at the generated c++ to get the exact identifier).

[Sirneij]

Thanks for the quick response. How then do we load the Datalog and fact files? And if I generate C++ code from the files, newInstance has nothing passed in:

namespace  souffle {
using namespace souffle;
class factory_Sf_tmp: souffle::ProgramFactory {
public:
souffle::SouffleProgram* newInstance();
 factory_Sf_tmp();
private:
};
} // namespace  souffle
namespace  souffle {
using namespace souffle;
souffle::SouffleProgram* factory_Sf_tmp::newInstance(){
return new  souffle::Sf_tmp();
}

 factory_Sf_tmp::factory_Sf_tmp():
souffle::ProgramFactory("tmp"){
}

} // namespace  souffle

Also, does it mean that one can't write a normal C++ program and use souffle to compile it without first generating a C++ code out of the Datalog programs? What does the C++ interface (https://souffle-lang.github.io/interface) do?

[quentin]

That's exact, the C++ interface provides functions to interact with c++ code generated by Souffle: populating input relations, running the program, reading output relations.

[Sirneij]

Thank you so much for the enlightment. I am sorry for the initial knowledge gap. I generated C++ from the datalog programs and used the interface to interact with the generated file. The name passed to the newInstance was the generated file's name, without its extension, and that worked.