1 files changed, 41 insertions, 0 deletions
diff --git a/lib/arel/algebra/predicates.rb b/lib/arel/algebra/predicates.rb
new file mode 100644
index 0000000000..72167c2b27
--- /dev/null
+++ b/lib/arel/algebra/predicates.rb
@@ -0,0 +1,41 @@
+module Arel
+  class Predicate
+    def or(other_predicate)
+      Or.new(self, other_predicate)
+    end
+
+    def and(other_predicate)
+      And.new(self, other_predicate)
+    end
+  end
+
+  class Binary < Predicate
+    attributes :operand1, :operand2
+    deriving :initialize
+
+    def ==(other)
+      self.class === other          and
+      @operand1  ==  other.operand1 and
+      @operand2  ==  other.operand2
+    end
+
+    def bind(relation)
+      self.class.new(operand1.find_correlate_in(relation), operand2.find_correlate_in(relation))
+    end
+  end
+
+  class Equality < Binary
+    def ==(other)
+      Equality === other and
+        ((operand1 == other.operand1 and operand2 == other.operand2) or
+         (operand1 == other.operand2 and operand2 == other.operand1))
+    end
+  end
+
+  class GreaterThanOrEqualTo  < Binary; end
+  class GreaterThan           < Binary; end
+  class LessThanOrEqualTo     < Binary; end
+  class LessThan              < Binary; end
+  class Match                 < Binary; end
+  class In                    < Binary; end
+end