8 files changed, 27 insertions, 39 deletions
diff --git a/lib/arel/algebra/relations/operations/join.rb b/lib/arel/algebra/relations/operations/join.rb
index dd67e8a9bf..9eee84113a 100644
--- a/lib/arel/algebra/relations/operations/join.rb
+++ b/lib/arel/algebra/relations/operations/join.rb
@@ -70,10 +70,4 @@ module Arel
       relation1.engine
     end
   end
-
-  module Relation
-    def join?
-      false
-    end
-  end
 end
diff --git a/lib/arel/algebra/relations/operations/order.rb b/lib/arel/algebra/relations/operations/order.rb
index 582abf642c..94bd7bcd59 100644
--- a/lib/arel/algebra/relations/operations/order.rb
+++ b/lib/arel/algebra/relations/operations/order.rb
@@ -31,5 +31,12 @@ module Arel
         engine
       end
     end
+
+    def eval
+      unoperated_rows.sort do |row1, row2|
+        ordering = orders.detect { |o| o.eval(row1, row2) != 0 } || orders.last
+        ordering.eval(row1, row2)
+      end
+    end
   end
 end
diff --git a/lib/arel/algebra/relations/operations/project.rb b/lib/arel/algebra/relations/operations/project.rb
index 2cdae288e3..daca742039 100644
--- a/lib/arel/algebra/relations/operations/project.rb
+++ b/lib/arel/algebra/relations/operations/project.rb
@@ -22,5 +22,9 @@ module Arel
         relation == other.relation &&
         projections == other.projections
     end
+
+    def eval
+      unoperated_rows.collect { |r| r.slice(*projections) }
+    end
   end
 end
diff --git a/lib/arel/algebra/relations/operations/skip.rb b/lib/arel/algebra/relations/operations/skip.rb
index f6a58d15bd..5a87fbb7b5 100644
--- a/lib/arel/algebra/relations/operations/skip.rb
+++ b/lib/arel/algebra/relations/operations/skip.rb
@@ -24,5 +24,9 @@ module Arel
         engine
       end
     end
+
+    def eval
+      unoperated_rows[skipped..-1]
+    end
   end
 end
diff --git a/lib/arel/algebra/relations/operations/take.rb b/lib/arel/algebra/relations/operations/take.rb
index 964aacacca..7098d578d5 100644
--- a/lib/arel/algebra/relations/operations/take.rb
+++ b/lib/arel/algebra/relations/operations/take.rb
@@ -28,5 +28,9 @@ module Arel
     def externalizable?
       true
     end
+
+    def eval
+      unoperated_rows[0, taken]
+    end
   end
 end
diff --git a/lib/arel/algebra/relations/operations/where.rb b/lib/arel/algebra/relations/operations/where.rb
index e8db2ec8b0..b447b18809 100644
--- a/lib/arel/algebra/relations/operations/where.rb
+++ b/lib/arel/algebra/relations/operations/where.rb
@@ -30,5 +30,9 @@ module Arel
         engine
       end
     end
+
+    def eval
+      unoperated_rows.select { |row| predicates.all? { |p| p.eval(row) } }
+    end
   end
 end
diff --git a/lib/arel/algebra/relations/relation.rb b/lib/arel/algebra/relations/relation.rb
index 3ed3a43503..17a2cf3190 100644
--- a/lib/arel/algebra/relations/relation.rb
+++ b/lib/arel/algebra/relations/relation.rb
@@ -6,6 +6,10 @@ module Arel
       Session.instance
     end
 
+    def join?
+      false
+    end
+
     def call
       engine.read(self)
     end
diff --git a/lib/arel/engines/memory/relations/operations.rb b/lib/arel/engines/memory/relations/operations.rb
index d026db460d..f233c48db0 100644
--- a/lib/arel/engines/memory/relations/operations.rb
+++ b/lib/arel/engines/memory/relations/operations.rb
@@ -1,37 +1,4 @@
 module Arel
-  class Where < Compound
-    def eval
-      unoperated_rows.select { |row| predicates.all? { |p| p.eval(row) } }
-    end
-  end
-
-  class Order < Compound
-    def eval
-      unoperated_rows.sort do |row1, row2|
-        ordering = orders.detect { |o| o.eval(row1, row2) != 0 } || orders.last
-        ordering.eval(row1, row2)
-      end
-    end
-  end
-
-  class Project < Compound
-    def eval
-      unoperated_rows.collect { |r| r.slice(*projections) }
-    end
-  end
-
-  class Take < Compound
-    def eval
-      unoperated_rows[0, taken]
-    end
-  end
-
-  class Skip < Compound
-    def eval
-      unoperated_rows[skipped..-1]
-    end
-  end
-
   class From < Compound
     def eval
       unoperated_rows[sources..-1]