Fun with ruby-prolog

prolog-family.rb

# gem install ruby-prolog
# https://github.com/preston/ruby-prolog/

# Prolog code:
#
# mother_child(trude, sally).
#
# father_child(tom, sally).
# father_child(tom, erica).
# father_child(mike, tom).
#
# sibling(X, Y)      :- parent_child(Z, X), parent_child(Z, Y).
#
# parent_child(X, Y) :- father_child(X, Y).
# parent_child(X, Y) :- mother_child(X, Y).
#
# sibling(sally, erica).
# => true

require 'ruby-prolog'

c = RubyProlog::Core.new
c.instance_eval do

  father_child['mike', 'tom'].fact
  father_child['tom', 'sally'].fact
  father_child['tom', 'erica'].fact
  mother_child['trude', 'sally'].fact


  parent_child[:X, :Y]  <<= [father_child[:X, :Y]]
  parent_child[:X, :Y]  <<= [mother_child[:X, :Y]]

  sibling[:X, :Y]       <<= [parent_child[:Z, :X], parent_child[:Z, :Y]]

  p query(sibling['sally', 'erica']) # => [[sibling["sally", "erica"]]]
  p query(sibling['trude', 'erica']) # => []

end