Implemented "alpha" and "opacity".

context.cpp

@@ -41,6 +41,9 @@ namespace Sass {
     register_function(mix_3_descriptor, mix_3);
     // HSL Functions
     register_function(invert_descriptor, invert);
+    // Opacity Functions
+    register_function(alpha_descriptor, alpha);
+    register_function(opacity_descriptor, alpha);
     // String Functions
     register_function(unquote_descriptor, unquote);
     register_function(quote_descriptor, quote);

functions.cpp

@@ -101,6 +101,16 @@ namespace Sass {
                   255 - orig[2].content.numeric_value,
                   orig[3].content.numeric_value);
     }
+    
+    // Opacity Functions ///////////////////////////////////////////////////
+    
+    Function_Descriptor alpha_descriptor =
+    { "alpha", "$color", 0 };
+    Function_Descriptor opacity_descriptor =
+    { "opacity", "$color", 0 };
+    Node alpha(const vector<Token>& parameters, map<Token, Node>& bindings) {
+      return bindings[parameters[0]][3];
+    }
       
     // String Functions ////////////////////////////////////////////////////
     

functions.hpp

@@ -72,6 +72,11 @@ namespace Sass {
     extern Function_Descriptor invert_descriptor;
     Node invert(const vector<Token>& parameters, map<Token, Node>& bindings);
     
+    // Opacity Functions ///////////////////////////////////////////////////
+    extern Function_Descriptor alpha_descriptor;
+    extern Function_Descriptor opacity_descriptor;
+    Node alpha(const vector<Token>& parameters, map<Token, Node>& bindings);
+    
     // String Functions ////////////////////////////////////////////////////
     extern Function_Descriptor unquote_descriptor;
     Node unquote(const vector<Token>& parameters, map<Token, Node>& bindings);