Source: gringo
Version: 5.1.0-4
Severity: serious
Tags: buster sid
User: debian...@lists.debian.org
Usertags: qa-ftbfs-20170805 qa-ftbfs
Justification: FTBFS on amd64

Hi,

During a rebuild of all packages in sid, your package failed to build on
amd64.

Relevant part (hopefully):
> g++ -o build/release/libgringo/src/python.o -c -g -O2 
> -fdebug-prefix-map=/<<PKGBUILDDIR>>=. -fstack-protector-strong -Wformat 
> -Werror=format-security -std=c++11 -O3 -Wall -Wdate-time -D_FORTIFY_SOURCE=2 
> -DNDEBUG -DNDEBUG=1 -DWITH_LUA=1 -DWITH_PYTHON=1 -I/usr/include/lua5.3 
> -I/usr/include/python2.7 -Ilibgringo -Ibuild/release/libgringo/src 
> -Ilibgringo/src -Ibuild/release/libreify -Ilibreify -Iliblp -Iliblp/src 
> libgringo/src/python.cc
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createId; PyCFunction 
> = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5664:33:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createId' is not a valid 
> template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createId; PyCFunction 
> = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createVariable; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5665:45:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createVariable' is not a 
> valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createVariable; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createSymbol; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5666:41:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createSymbol' is not a 
> valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createSymbol; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createUnaryOperation; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5667:57:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createUnaryOperation' is 
> not a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createUnaryOperation; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createBinaryOperation; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5668:59:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createBinaryOperation' 
> is not a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createBinaryOperation; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createInterval; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5669:45:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createInterval' is not a 
> valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createInterval; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createFunction; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5670:45:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createFunction' is not a 
> valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createFunction; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createPool; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5671:37:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createPool' is not a 
> valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createPool; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createCSPProduct; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5672:49:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createCSPProduct' is not 
> a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createCSPProduct; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createCSPSum; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5673:41:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createCSPSum' is not a 
> valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createCSPSum; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createCSPGuard; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5674:45:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createCSPGuard' is not a 
> valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createCSPGuard; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createBooleanConstant; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5675:59:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createBooleanConstant' 
> is not a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createBooleanConstant; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createSymbolicAtom; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5676:53:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createSymbolicAtom' is 
> not a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createSymbolicAtom; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createComparison; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5677:49:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createComparison' is not 
> a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createComparison; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createCSPLiteral; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5678:49:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createCSPLiteral' is not 
> a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createCSPLiteral; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createAggregateGuard; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5679:57:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createAggregateGuard' is 
> not a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createAggregateGuard; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = 
> Gringo::{anonymous}::createConditionalLiteral; PyCFunction = _object* 
> (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5680:65:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createConditionalLiteral'
>  is not a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = 
> Gringo::{anonymous}::createConditionalLiteral; PyCFunction = _object* 
> (*)(_object*, _object*); PyObject = _object]' not a return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createAggregate; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5681:47:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createAggregate' is not 
> a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createAggregate; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = 
> Gringo::{anonymous}::createBodyAggregateElement; PyCFunction = _object* 
> (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5682:69:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createBodyAggregateElement'
>  is not a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = 
> Gringo::{anonymous}::createBodyAggregateElement; PyCFunction = _object* 
> (*)(_object*, _object*); PyObject = _object]' not a return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createBodyAggregate; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5683:55:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createBodyAggregate' is 
> not a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createBodyAggregate; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = 
> Gringo::{anonymous}::createHeadAggregateElement; PyCFunction = _object* 
> (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5684:69:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createHeadAggregateElement'
>  is not a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = 
> Gringo::{anonymous}::createHeadAggregateElement; PyCFunction = _object* 
> (*)(_object*, _object*); PyObject = _object]' not a return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createHeadAggregate; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5685:55:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createHeadAggregate' is 
> not a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createHeadAggregate; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createDisjunction; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5686:51:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createDisjunction' is 
> not a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createDisjunction; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createDisjointElement; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5687:59:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createDisjointElement' 
> is not a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createDisjointElement; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createDisjoint; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5688:45:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createDisjoint' is not a 
> valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createDisjoint; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createTheoryFunction; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5689:57:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createTheoryFunction' is 
> not a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createTheoryFunction; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createTheorySequence; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5690:57:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createTheorySequence' is 
> not a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createTheorySequence; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = 
> Gringo::{anonymous}::createTheoryUnparsedTermElement; PyCFunction = _object* 
> (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5691:79:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createTheoryUnparsedTermElement'
>  is not a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = 
> Gringo::{anonymous}::createTheoryUnparsedTermElement; PyCFunction = _object* 
> (*)(_object*, _object*); PyObject = _object]' not a return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = 
> Gringo::{anonymous}::createTheoryUnparsedTerm; PyCFunction = _object* 
> (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5692:65:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createTheoryUnparsedTerm'
>  is not a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = 
> Gringo::{anonymous}::createTheoryUnparsedTerm; PyCFunction = _object* 
> (*)(_object*, _object*); PyObject = _object]' not a return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createTheoryGuard; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5693:51:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createTheoryGuard' is 
> not a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createTheoryGuard; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = 
> Gringo::{anonymous}::createTheoryAtomElement; PyCFunction = _object* 
> (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5694:63:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createTheoryAtomElement' 
> is not a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = 
> Gringo::{anonymous}::createTheoryAtomElement; PyCFunction = _object* 
> (*)(_object*, _object*); PyObject = _object]' not a return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createTheoryAtom; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5695:49:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createTheoryAtom' is not 
> a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createTheoryAtom; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createLiteral; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5696:43:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createLiteral' is not a 
> valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createLiteral; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = 
> Gringo::{anonymous}::createTheoryOperatorDefinition; PyCFunction = _object* 
> (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5697:77:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createTheoryOperatorDefinition'
>  is not a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = 
> Gringo::{anonymous}::createTheoryOperatorDefinition; PyCFunction = _object* 
> (*)(_object*, _object*); PyObject = _object]' not a return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = 
> Gringo::{anonymous}::createTheoryTermDefinition; PyCFunction = _object* 
> (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5698:69:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createTheoryTermDefinition'
>  is not a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = 
> Gringo::{anonymous}::createTheoryTermDefinition; PyCFunction = _object* 
> (*)(_object*, _object*); PyObject = _object]' not a return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = 
> Gringo::{anonymous}::createTheoryGuardDefinition; PyCFunction = _object* 
> (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5699:71:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createTheoryGuardDefinition'
>  is not a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = 
> Gringo::{anonymous}::createTheoryGuardDefinition; PyCFunction = _object* 
> (*)(_object*, _object*); PyObject = _object]' not a return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = 
> Gringo::{anonymous}::createTheoryAtomDefinition; PyCFunction = _object* 
> (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5700:69:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createTheoryAtomDefinition'
>  is not a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = 
> Gringo::{anonymous}::createTheoryAtomDefinition; PyCFunction = _object* 
> (*)(_object*, _object*); PyObject = _object]' not a return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = 
> Gringo::{anonymous}::createTheoryDefinition; PyCFunction = _object* 
> (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5701:61:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createTheoryDefinition' 
> is not a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = 
> Gringo::{anonymous}::createTheoryDefinition; PyCFunction = _object* 
> (*)(_object*, _object*); PyObject = _object]' not a return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createRule; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5702:37:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createRule' is not a 
> valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createRule; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createDefinition; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5703:49:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createDefinition' is not 
> a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createDefinition; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createShowSignature; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5704:55:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createShowSignature' is 
> not a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createShowSignature; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createShowTerm; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5705:45:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createShowTerm' is not a 
> valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createShowTerm; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createMinimize; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5706:45:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createMinimize' is not a 
> valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createMinimize; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createScript; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5707:41:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createScript' is not a 
> valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createScript; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createProgram; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5708:43:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createProgram' is not a 
> valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createProgram; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createExternal; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5709:45:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createExternal' is not a 
> valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createExternal; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createEdge; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5710:37:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createEdge' is not a 
> valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createEdge; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createHeuristic; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5711:47:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createHeuristic' is not 
> a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createHeuristic; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createProjectAtom; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5712:51:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createProjectAtom' is 
> not a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::createProjectAtom; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = 
> Gringo::{anonymous}::createProjectSignature; PyCFunction = _object* 
> (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:5713:61:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::createProjectSignature' 
> is not a valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = 
> Gringo::{anonymous}::createProjectSignature; PyCFunction = _object* 
> (*)(_object*, _object*); PyObject = _object]' not a return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> libgringo/src/python.cc: In instantiation of 'constexpr PyObject* (* 
> Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::parseProgram; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]':
> libgringo/src/python.cc:6021:48:   required from here
> libgringo/src/python.cc:348:46: error: '*(Gringo::{anonymous}::Object 
> (*)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference))Gringo::{anonymous}::parseProgram' is not a 
> valid template argument for type 'Gringo::{anonymous}::Object 
> (&)(Gringo::{anonymous}::Reference, Gringo::{anonymous}::Reference)'
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                               
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> libgringo/src/python.cc:348:46: note: it must be the name of a function with 
> external linkage
> libgringo/src/python.cc:348:99: error: body of constexpr function 'constexpr 
> PyObject* (* Gringo::{anonymous}::to_function())(PyObject*, PyObject*) [with 
> Gringo::{anonymous}::Object (& f)(Gringo::{anonymous}::Reference, 
> Gringo::{anonymous}::Reference) = Gringo::{anonymous}::parseProgram; 
> PyCFunction = _object* (*)(_object*, _object*); PyObject = _object]' not a 
> return-statement
>  constexpr PyCFunction to_function() { return 
> reinterpret_cast<PyCFunction>(ToFunction<f>::value); }
>                                                                               
>                      ^
> scons: *** [build/release/libgringo/src/python.o] Error 1
> scons: building terminated because of errors.
> debian/rules:67: recipe for target 'override_dh_auto_build' failed
> make[1]: *** [override_dh_auto_build] Error 2

The full build log is available from:
   http://aws-logs.debian.net/2017/08/05/gringo_5.1.0-4_unstable.log

A list of current common problems and possible solutions is available at
http://wiki.debian.org/qa.debian.org/FTBFS . You're welcome to contribute!

About the archive rebuild: The rebuild was done on EC2 VM instances from
Amazon Web Services, using a clean, minimal and up-to-date chroot. Every
failed build was retried once to eliminate random failures.

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