Allowing calls to non-Sass functions to pass through. Apparently this is allowed.

src/document_parser.cpp

@@ -655,13 +655,13 @@ namespace Sass {
       if (!lex< exactly<')'> >()) syntax_error("unclosed parenthesis");
       return value;
     }
-    else if (lex< exactly<'+'> >()) {
+    else if (lex< sequence< exactly<'+'>, negate< number > > >()) {
       Node plus(Node::unary_plus, context.registry, line_number, 1);
       plus << parse_factor();
       plus.eval_me = true;
       return plus;
     }
-    else if (lex< exactly<'-'> >()) {
+    else if (lex< sequence< exactly<'-'>, negate< number> > >()) {
       Node minus(Node::unary_minus, context.registry, line_number, 1);
       minus << parse_factor();
       minus.eval_me = true;

src/eval_apply.cpp

@@ -216,9 +216,10 @@ namespace Sass {
         // TO DO: default-constructed Function should be a generic callback
         pair<string, size_t> sig(expr[0].content.token.to_string(), expr[1].size());
         if (!f_env.count(sig)) {
-          stringstream ss;
-          ss << "no function named " << expr[0].content.token.to_string() << " taking " << expr[1].size() << " arguments has been defined";
-          eval_error(ss.str(), expr.line_number, expr.file_name);
+          // stringstream ss;
+          // ss << "no function named " << expr[0].content.token.to_string() << " taking " << expr[1].size() << " arguments has been defined";
+          // eval_error(ss.str(), expr.line_number, expr.file_name);
+          return expr;
         }
         return apply_function(f_env[sig], expr[1], env, f_env, registry);
       } break;

src/node.cpp

@@ -174,6 +174,27 @@ namespace Sass {
         return "/";
       } break;
       
+      case function_call: {
+        stringstream ss;
+        ss << at(0).to_string("");
+        ss << "(";
+        ss << at(1).to_string("");
+        ss << ")";
+        return ss.str();
+      }
+      
+      case arguments: {
+        stringstream ss;
+        if (size() > 0) {
+          ss << at(0).to_string("");
+          for (int i = 1; i < size(); ++i) {
+            ss << ", ";
+            ss << at(i).to_string("");
+          }
+        }
+        return ss.str();
+      }
+      
       case unary_plus: {
         stringstream ss;
         ss << "+";