Updates to the ASTNode class.

Added some checks for re-definition for values and children.
Removed the requirement that values not be instances of ASTNodes.

README.md

@@ -485,7 +485,7 @@ class BinOp < Expression
 end
 ```
 
-The assignment functions that are generated for the children and values perform type checking to make sure that the AST is well-formed.  The type of a child must be a subclass of the {RLTK::ASTNode} class, whereas the type of a value must **NOT** be a subclass of the {RLTK::ASTNode} class.  While child and value objects are stored as instance variables it is unsafe to assign to these variables directly, and it is strongly recommended to always use the accessor functions.
+The assignment functions that are generated for the children and values perform type checking to make sure that the AST is well-formed.  The type of a child must be a subclass of the {RLTK::ASTNode} class, whereas the type of a value can be any Ruby class.  While child and value objects are stored as instance variables it is unsafe to assign to these variables directly, and it is strongly recommended to always use the accessor functions.
 
 When instantiating a subclass of {RLTK::ASTNode} the arguments to the constructor should be the node's values (in order of definition) followed by the node's children (in order of definition).  If a constructor is given fewer arguments then the number of values and children the remaining arguments are assumed to be `nil`.  Example:
 

TODO.md

@@ -40,9 +40,6 @@ Whole Project
 Ruby Only
 ---------
 
-* Allow ASTNode values to be subclasses of ASTNode (for reference nodes)
-* Emit a warning when re-defining a value or child element of an AST node
-
 * Double check parse table production method against LALR/LR table production
   * Check lookahead pruning method to see if generating LALR(1) or LR(1) parser
   * If we are generating LR(1) parser, correct documentation

lib/rltk/ast.rb

@@ -36,6 +36,19 @@ class ASTNode
 
 		class << self
 
+			# Check to make sure a name isn't re-defining a value or child.
+			#
+			# @raise [ArgumentError]  Raised if the name is already used for an existing value or child
+			def check_odr(name)
+				if @child_names.include? name
+					raise ArgumentError, "Class #{self} or one of its superclasses already defines a child named #{name}"
+				end
+
+				if @value_names.include?(name)
+					raise ArgumentError, "Class #{self} or one of its superclasses already defines a value named #{name}"
+				end
+			end
+
 			# Installs instance class varialbes into a class.
 			#
 			# @return [void]
@@ -74,6 +87,8 @@ def inherited(klass)
 			#
 			# @return [void]
 			def child(name, type)
+				check_odr(name)
+
 				if type.is_a?(Array) and type.length == 1
 					t = type.first
 
@@ -151,14 +166,15 @@ def define_accessor(name, type, set_parent = false)
 
 			# Defined a value for this AST class and its subclasses.
 			# The name of the value will be used to define accessor
-			# methods that include type checking.  The type of this
-			# value must NOT be a subclass of the ASTNode class.
+			# methods that include type checking.
 			#
 			# @param [String, Symbol]  name  Name of value
-			# @param [Class]           type  Type of value; Must NOT be a subclass of ASTNode
+			# @param [Class]           type  Type of value
 			#
 			# @return [void]
 			def value(name, type)
+				check_odr(name)
+
 				if type.is_a?(Array) and type.length == 1
 					t = type.first
 
@@ -169,12 +185,6 @@ def value(name, type)
 					raise 'Child and Value types must be a class name or an array with a single class name element.'
 				end
 
-				# Check to make sure that type is NOT a subclass of
-				# ASTNode.
-				if t.subclass_of?(ASTNode)
-					raise "A value's type specification must NOT be a subclass of ASTNode."
-				end
-
 				@value_names << name
 				@value_types << type
 				define_accessor(name, type)

test/tc_ast.rb

@@ -116,20 +116,6 @@ def test_copy
 		assert_equal(@tree5, new_tree)
 	end
 
-	def test_value
-		node = VNode.new
-
-		assert_equal(node.values, [nil, nil])
-
-		node.values = (expected_values = [42, 1984])
-
-		assert_equal(node.values, expected_values)
-
-		node.values = (expected_values = {:a => 1984, :b => 42})
-
-		assert_equal(node.values(Hash), expected_values)
-	end
-
 	def test_dump
 		tree0_string = @tree0.dump
 
@@ -236,8 +222,34 @@ def test_notes
 		assert_nil(node[:a])
 	end
 
+	def test_one_definition_rule
+		asserter = self
+
+		Class.new(ANode) do
+			asserter.assert_raises(ArgumentError) { child :left, ANode }
+		end
+
+		Class.new(ENode) do
+			asserter.assert_raises(ArgumentError) { value :str, String }
+		end
+	end
+
 	def test_root
 		assert_same(@tree0, @tree0.root)
 		assert_same(@tree0, @leaf0.root)
 	end
+
+	def test_value
+		node = VNode.new
+
+		assert_equal(node.values, [nil, nil])
+
+		node.values = (expected_values = [42, 1984])
+
+		assert_equal(node.values, expected_values)
+
+		node.values = (expected_values = {:a => 1984, :b => 42})
+
+		assert_equal(node.values(Hash), expected_values)
+	end
 end