diff --git a/TODO.txt b/TODO.txt
index c0c7e02..2dfb4c5 100644
--- a/TODO.txt
+++ b/TODO.txt
@@ -2,3 +2,4 @@ Test RuneReader
 Test Regexp
 Add SPDX tags
 What's Megaparsec got that we ain't got?
+Add Do parser that runs an action on the result of the previous parser.
diff --git a/gigaparsec.go b/gigaparsec.go
index e07bd31..051f174 100644
--- a/gigaparsec.go
+++ b/gigaparsec.go
@@ -125,6 +125,20 @@ func (s State[In]) At(pos uint64) State[In] {
 
 type Parser[In, Out any] func(State[In]) (Result[In, Out], error)
 
+func (p Parser[In, Out]) Label(label string) Parser[In, Out] {
+	return func(input State[In]) (Result[In, Out], error) {
+		result, err := p(input)
+		if err != nil || result.Consumed() {
+			return result, err
+		}
+		if succeeded, _, value, next, msg := result.Succeeded(); succeeded {
+			return Succeed(false, value, next, msg.expect(label)), nil
+		}
+		_, _, msg := result.Failed()
+		return Fail[In, Out](false, msg.expect(label)), nil
+	}
+}
+
 func Return[In, Out any](value Out) Parser[In, Out] {
 	return func(state State[In]) (Result[In, Out], error) {
 		return Succeed(false, value, state, MessageOK(state.Pos())), nil
@@ -246,20 +260,6 @@ func Try[In, Out any](p Parser[In, Out]) Parser[In, Out] {
 	}
 }
 
-func Label[In, Out any](p Parser[In, Out], l string) Parser[In, Out] {
-	return func(input State[In]) (Result[In, Out], error) {
-		result, err := p(input)
-		if err != nil || result.Consumed() {
-			return result, err
-		}
-		if succeeded, _, value, next, msg := result.Succeeded(); succeeded {
-			return Succeed(false, value, next, msg.expect(l)), nil
-		}
-		_, _, msg := result.Failed()
-		return Fail[In, Out](false, msg.expect(l)), nil
-	}
-}
-
 func Map[In, Out1, Out2 any](p Parser[In, Out1], f func(Out1) Out2) Parser[In, Out2] {
 	return Bind(p, func(out Out1) Parser[In, Out2] {
 		return Return[In](f(out))