Moved register state to scopes

src/build/expression/Expression.go

@@ -32,6 +32,21 @@ func (expr *Expression) AddChild(child *Expression) {
 	child.Parent = expr
 }
 
+// Count counts how often the given token appears in the expression.
+func (expr *Expression) Count(kind token.Kind, name string) int {
+	count := 0
+
+	expr.EachLeaf(func(leaf *Expression) error {
+		if leaf.Token.Kind == kind && leaf.Token.Text() == name {
+			count++
+		}
+
+		return nil
+	})
+
+	return count
+}
+
 // Reset resets all values to the default.
 func (expr *Expression) Reset() {
 	for _, child := range expr.Children {