diff --git a/lexer/lexer.go b/lexer/lexer.go
index 33b17b6..e23ecad 100644
--- a/lexer/lexer.go
+++ b/lexer/lexer.go
@@ -1,2 +1,22 @@
 // Package lexer provides basic helpers to implement parsers
 package lexer
+
+// StateFn is a State Function of the parser
+type StateFn func() (StateFn, error)
+
+// Run runs a state machine until the state function either
+// returns nil or an error
+func Run(fn StateFn) error {
+	for fn != nil {
+		var err error
+
+		fn, err = fn()
+		if err != nil {
+			// failed
+			return err
+		}
+	}
+
+	// ended
+	return nil
+}