Fast single byte matcher

parser.go

@@ -81,6 +81,21 @@ func ParseString(parser Parserish, input string) (result interface{}, remaining
 }
 
 func Exact(match string) Parser {
+	if len(match) == 1 {
+		matchByte := match[0]
+		return NewParser(match, func(ps *State) Node {
+			ps.AutoWS()
+			if ps.Input[ps.Pos] != matchByte {
+				ps.ErrorHere(match)
+				return Node{}
+			}
+
+			ps.Advance(1)
+
+			return Node{Token: match}
+		})
+	}
+
 	return NewParser(match, func(ps *State) Node {
 		ps.AutoWS()
 		if !strings.HasPrefix(ps.Get(), match) {

parser_test.go

@@ -49,17 +49,29 @@ func TestParsifyAll(t *testing.T) {
 }
 
 func TestExact(t *testing.T) {
-	t.Run("success", func(t *testing.T) {
+	t.Run("success string", func(t *testing.T) {
 		node, ps := runParser("foobar", Exact("fo"))
 		require.Equal(t, "fo", node.Token)
 		require.Equal(t, "obar", ps.Get())
 	})
 
+	t.Run("success char", func(t *testing.T) {
+		node, ps := runParser("foobar", Exact("f"))
+		require.Equal(t, "f", node.Token)
+		require.Equal(t, "oobar", ps.Get())
+	})
+
 	t.Run("error", func(t *testing.T) {
 		_, ps := runParser("foobar", Exact("bar"))
 		require.Equal(t, "bar", ps.Error.Expected)
 		require.Equal(t, 0, ps.Pos)
 	})
+
+	t.Run("error char", func(t *testing.T) {
+		_, ps := runParser("foobar", Exact("o"))
+		require.Equal(t, "o", ps.Error.Expected)
+		require.Equal(t, 0, ps.Pos)
+	})
 }
 
 func TestChars(t *testing.T) {