SWIPL

A Ruby Gem for binding to SWI Prolog. This uses Ruby's FFI gem for binding.

Add this line to your application's Gemfile:

gem 'swipl'

Set SWI_LIB to the where you have the libswipl.{dylib,so,dll} file. Unforunately I haven't figured out a better method for locating the library; open to ideas and pull requests to make this easier for client applications.

Please see SWIPL::CFFI for more advanced use cases.

You can query if a statement is truthy by passing it as string as follows:

SWIPL::verify('true')

This will boot up the engine and run the query the Prolog for the answer. Your programs can be arbitrarily complex, however this will only result in true or false.

Let's say you have the following prolog database in foods.pl:

food( beef ).
food( broccoli ).
food( potatoes ).

enjoys( mark, broccoli ).

You can they load the database (assuming in the same directory) an query for all solutions as follows:

SWIPL::truth( "consult('foods.pl')" )
foods = SWIPL::query( "food", 1 )

The variable foods should now contain the follow (note: order of the elements may change):

[ ["beef"], ["broccoli"], ["potatoes"] ]

This is kind of a gnarly API right now. My goal is to clean it up, but querying with bound variables is possible right now.

SWIPL::PrologFrame.on do |frame|
	human = frame.atom_from_string( "mark" )
	predicate = SWIPL::Predicate.find( "enjoys", 2 )
	query = predicate.query_normally_with( frame, [human, nil ] ) # nil will result in an unground variable
	begin
		query.each_solution do |solution|
			puts solution
		end
	ensure
		query.close # if you forget this there will probably be some strange statement about no foreign frame
	end
end

Resulting output:

["mark", "broccoli"]

SWIPL::deterministic "always_true", 0 do
	SWIPL::PL_TRUE
end

SWIPL::verify( "always_true" ) == true

Bug reports and pull requests are welcome on GitHub at https://github.com/meschbach/gem-swipl.

The gem is available as open source under the terms of the MIT License.