[Sass] Add an abstract superclass for SassScript parse-tree nodes.

lib/sass/script.rb

@@ -1,4 +1,5 @@
 require 'strscan'
+require 'sass/script/node'
 require 'sass/script/variable'
 require 'sass/script/funcall'
 require 'sass/script/operation'
@@ -42,8 +43,7 @@ module Sass
     #   Used for error reporting
     # @param filename [String] The path to the file in which the SassScript appeared.
     #   Used for error reporting
-    # @return [#perform(Sass::Environment)] The root node of the parse tree,
-    #   for example {Operation}
+    # @return [Script::Node] The root node of the parse tree
     def self.parse(value, line, offset, filename = nil)
       Parser.parse(value, line, offset, filename)
     rescue Sass::SyntaxError => e

lib/sass/script/funcall.rb

@@ -6,7 +6,7 @@ module Sass
     # A function call either calls one of the functions in {Script::Functions},
     # or if no function with the given name exists
     # it returns a string representation of the function call.
-    class Funcall
+    class Funcall < Node
       # The name of the function.
       #
       # @return [String]
@@ -14,11 +14,11 @@ module Sass
 
       # The arguments to the function.
       #
-      # @return [Array<#perform(Sass::Environment)>]
+      # @return [Array<Script::Node>]
       attr_reader :args
 
       # @param name [String] See \{#name}
-      # @param name [Array<#perform(Sass::Environment)>] See \{#args}
+      # @param name [Array<Script::Node>] See \{#args}
       def initialize(name, args)
         @name = name
         @args = args

lib/sass/script/literal.rb

@@ -4,7 +4,7 @@ module Sass::Script
   # Many of these methods, especially the ones that correspond to SassScript operations,
   # are designed to be overridden by subclasses which may change the semantics somewhat.
   # The operations listed here are just the defaults.
-  class Literal
+  class Literal < Node
     require 'sass/script/string'
     require 'sass/script/number'
     require 'sass/script/color'

lib/sass/script/node.rb

@@ -0,0 +1,14 @@
+module Sass::Script
+  # The abstract superclass for SassScript parse tree nodes.
+  #
+  # Use \{#perform} to evaluate a parse tree.
+  class Node
+    # Evaluates the node.
+    #
+    # @param environment [Sass::Environment] The environment in which to evaluate the SassScript
+    # @return [Literal] The SassScript object that is the value of the SassScript
+    def perform(environment)
+      raise NotImplementedError.new("All subclasses of Sass::Script::Node must override #perform.")
+    end
+  end
+end

lib/sass/script/operation.rb

@@ -8,10 +8,10 @@ require 'sass/script/unary_operation'
 module Sass::Script
   # A SassScript parse node representing a binary operation,
   # such as `!a + !b` or `"foo" + 1`.
-  class Operation
-    # @param operand1 [#perform(Sass::Environment)] The parse-tree node
+  class Operation < Node
+    # @param operand1 [Script::Node] The parse-tree node
     #   for the right-hand side of the operator
-    # @param operand2 [#perform(Sass::Environment)] The parse-tree node
+    # @param operand2 [Script::Node] The parse-tree node
     #   for the left-hand side of the operator
     # @param operator [Symbol] The operator to perform.
     #   This should be one of the binary operator names in {Lexer::OPERATORS}

lib/sass/script/parser.rb

@@ -3,9 +3,7 @@ require 'sass/script/lexer'
 module Sass
   module Script
     # The parser for SassScript.
-    # It parses a string of code into a tree of nodes
-    # such as {Operation} that can then have #perform
-    # called to create the resulting {Literal}.
+    # It parses a string of code into a tree of {Script::Node}s.
     class Parser
       # @param str [String, StringScanner] The source text to parse
       # @param line [Fixnum] The line on which the SassScript appears.
@@ -24,8 +22,7 @@ module Sass
       # which signals the end of an interpolated segment,
       # it returns rather than throwing an error.
       #
-      # @return [#perform(Sass::Environment)] The root node of the parse tree,
-      #   for example {Operation}
+      # @return [Script::Node] The root node of the parse tree
       # @raise [Sass::SyntaxError] if the expression isn't valid SassScript
       def parse_interpolated
         expr = assert_expr :expr
@@ -35,8 +32,7 @@ module Sass
 
       # Parses a SassScript expression.
       #
-      # @return [#perform(Sass::Environment)] The root node of the parse tree,
-      #   for example {Operation}
+      # @return [Script::Node] The root node of the parse tree
       # @raise [Sass::SyntaxError] if the expression isn't valid SassScript
       def parse
         expr = assert_expr :expr
@@ -47,8 +43,7 @@ module Sass
       # Parses a SassScript expression.
       #
       # @call-seq parse(str, line, offset, filename = nil)
-      # @return [#perform(Sass::Environment)] The root node of the parse tree,
-      #   for example {Operation}
+      # @return [Script::Node] The root node of the parse tree
       # @see Parser#initialize
       # @see Parser#parse
       def self.parse(*args)

lib/sass/script/unary_operation.rb

@@ -3,8 +3,8 @@ module Sass::Script
   # such as `-!b` or `not true`.
   #
   # Currently only `-`, `/`, and `not` are unary operators.
-  class UnaryOperation
-    # @param operand [#perform(Sass::Environment)] The parse-tree node
+  class UnaryOperation < Node
+    # @param operand [Script::Node] The parse-tree node
     #   for the object of the operator
     # @param operator [Symbol] The operator to perform
     def initialize(operand, operator)

lib/sass/script/variable.rb

@@ -1,7 +1,7 @@
 module Sass
   module Script
     # A SassScript parse node representing a variable.
-    class Variable
+    class Variable < Node
       # The name of the variable.
       #
       # @return [String]

lib/sass/tree/node.rb

@@ -6,7 +6,7 @@ module Sass
   # and for loops and so forth,
   # in addition to nodes for CSS rules and properties.
   #
-  # However, {Node#perform} returns a different sort of tree.
+  # However, {Tree::Node#perform} returns a different sort of tree.
   # This tree maps more closely to the resulting CSS document
   # than it does to the original Sass document.
   # It still has nodes for CSS rules and properties,
@@ -20,7 +20,7 @@ module Sass
     class Node
       # The child nodes of this node.
       #
-      # @return [Array<Node>]
+      # @return [Array<Tree::Node>]
       attr_accessor :children
 
       # The line of the document on which this node appeared.
@@ -43,7 +43,7 @@ module Sass
 
       # Appends a child to the node.
       #
-      # @param child [Node] The child node
+      # @param child [Tree::Node] The child node
       # @raise [Sass::SyntaxError] if `child` is invalid
       # @see #invalid_child?
       def <<(child)
@@ -55,14 +55,14 @@ module Sass
 
       # Return the last child node.
       #
-      # We need this because {Node} duck types as an Array for {Sass::Engine}.
+      # We need this because {Tree::Node} duck types as an Array for {Sass::Engine}.
       #
-      # @return [Node] The last child node
+      # @return [Tree::Node] The last child node
       def last
         children.last
       end
 
-      # Compares this node and another object (only other {Node}s will be equal).
+      # Compares this node and another object (only other {Tree::Node}s will be equal).
       # This does a structural comparison;
       # if the contents of the nodes and all the child nodes are equivalent,
       # then the nodes are as well.
@@ -107,7 +107,7 @@ module Sass
       #
       # @param environment [Sass::Environment] The lexical environment containing
       #   variable and mixin values
-      # @return [Node] The resulting tree of static nodes
+      # @return [Tree::Node] The resulting tree of static nodes
       # @raise [Sass::SyntaxError] if some element of the tree is invalid
       # @see Sass::Tree
       def perform(environment)
@@ -124,7 +124,7 @@ module Sass
       #
       # @param environment [Sass::Environment] The lexical environment containing
       #   variable and mixin values
-      # @return [Node, Array<Node>] The resulting static nodes
+      # @return [Tree::Node, Array<Tree::Node>] The resulting static nodes
       # @see #perform
       # @see Sass::Tree
       def _perform(environment)
@@ -148,7 +148,7 @@ module Sass
       #
       # @param environment [Sass::Environment] The lexical environment containing
       #   variable and mixin values
-      # @return [Array<Node>] The resulting static nodes
+      # @return [Array<Tree::Node>] The resulting static nodes
       def perform_children(environment)
         children.map {|c| c.perform(environment)}.flatten
       end
@@ -191,7 +191,7 @@ module Sass
       # This is expected to be overriden by subclasses
       # for which some children are invalid.
       #
-      # @param child [Node] A potential child node
+      # @param child [Tree::Node] A potential child node
       # @return [Boolean, String] Whether or not the child node is valid,
       #   as well as the error message to display if it is invalid
       def invalid_child?(child)