Added beginning support for calc however, the expression is not fully parsed into the AST.

lib/src/tree.dart

Index: lib/src/tree.dart
diff --git a/lib/src/tree.dart b/lib/src/tree.dart
index 75e962900085a6f953f4e4bbd8263d184d47391b..b8438bbfb70043f9c87aa15ccefe2a767d720fae 100644
--- a/lib/src/tree.dart
+++ b/lib/src/tree.dart
@@ -44,6 +44,21 @@ class Negation extends TreeNode {
   String get name => 'not';
 }
 
+// calc(...)
+// TODO(terry): Hack to handle calc however the expressions should be fully
+//              parsed and in the AST.
+class CalcTerm extends LiteralTerm {
+  final LiteralTerm expr;
+
+  CalcTerm(var value, String t, this.expr, SourceSpan span)
+      : super(value, t, span);
+
+  CalcTerm clone() => new CalcTerm(value, text, expr.clone(), span);
+  visit(VisitorBase visitor) => visitor.visitCalcTerm(this);
+
+  String toString() => "$t($expr)";

[kevmoo, 2015/10/16 17:56:39]

Where is `t` coming from? you mean `$text`?

[terry, 2015/10/16 18:28:47]

Done.

+}
+
 // /*  ....   */
 class CssComment extends TreeNode {
   final String comment;