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A Rubyish DSL for Logic Programming

Posted by Jamis on November 06, 2006 @ 11:37 AM

Alright, I had a rather productive weekend. After mentioning in my post about Prolog in Ruby that it would be nice to have a more Rubyish implementation, I started hammering away on an implementation of my own.

The result:

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db = KBase::Database.new do
  + X.is_sibling_of(Y).if { Z.is_parent_of(X) & Z.is_parent_of(Y) & X.is_not(Y) }
  + X.is_parent_of(Y).if { X.is_father_of(Y) }
  + X.is_parent_of(Y).if { X.is_mother_of(Y) }

  + jamis.is_father_of(kaitrin)
  + jamis.is_father_of(nathaniel)
end

result = db.query { nathaniel.is_sibling_of(X) }
puts "querying #{result.goal}..."
result.each do |solution|
  puts "solution:"
  solution.bindings.each do |variable, value|
    puts " - #{variable}: #{value}"
  end
end
puts "no solutions!" if result.empty?

The output from the above program:

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$ ruby resolver.rb
querying nathaniel.is_sibling_of(X)...
solution:
 - X: kaitrin
$

I’ll be cleaning it up next, and will write about the implementation of the DSL. It was a fun project! Honestly, though, the DSL was the easy part…the hard part was getting the prolog-like matching and backtracking working. It’s still not perfect, but it works for queries like the above.

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Comments

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06 Nov 2006

1. Seth Ladd said...

Nice work! Would be interesting to hook this up to ActiveRDF and implement some RDFS and OWL rules.