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Example: Vectors of Numbers |
This is an example of using the low-level interface.
In the Prolog client:
vector_type(double(_List), 2). vector_type(float(_List), 3). vector_type(integer(_List), 4). vector_type(integer64(_List), 5). vector_type(integer32(_List), 6). vector_type(unsigned(_List), 7). vector_type(codes(_List), 8). vector_type(atom(_List), 9). vector_type(string(_List), 10). vector(Type, B):- vector_type(Type, Tag), Proto = protobuf([ repeated(Tag, Type) ]), protobuf_message(Proto, B).
A protobuf description that is compatible with the above wire stream follows:
message Vector { repeated double double_values = 2; repeated float float_values = 3; repeated sint32 integer_values = 4; repeated fixed64 integer64_values = 5; repeated fixed32 integer32_values = 6; repeated uint32 unsigned_values = 7; repeated bytes bytes_values = 8; repeated string atom_values = 9; repeated string string_values = 10; }
A typical application might consist of an abstract adapter class along with a collection of concrete subclasses that refine an abstract behavior in order to hide the interaction with the underlying protobuf interpreter. An example of such a class written in C++ may be found in the demos.
On the Prolog side:
:- meta_predicate ~>(0,0). :- op(950, xfy, ~>). ~>(P, Q) :- setup_call_cleanup(P, (true; fail), assertion(Q)). write_as_proto(Vector) :- vector(Vector, WireStream), open('tmp99.tmp', write, S, [encoding(octet),type(binary)]) ~> close(S), format(S, '~s', [WireStream]), !. testv1(V) :- read_file_to_codes('tmp99.tmp', Codes, [encoding(octet),type(binary)]), vector(V, Codes).
Run the Prolog side:
?- X is pi, write_as_proto(double([-2.2212, -7.6675, X, 0, 1.77e-9, 2.54e222])). X = 3.14159. ?- testv1(Vector). Vector = double([-2.2212, -7.6675, 3.14159, 0.0, 1.77e-09, 2.54e+222]) ?-
Verify the wire stream using the protobuf compiler's decoder:
$ protoc --decode=Vector pb_vector.proto <tmp99.tmp double_values: -2.2212 double_values: -7.6675 double_values: 3.1415926535897931 double_values: 0 double_values: 1.77e-09 double_values: 2.5400000000000002e+222