examples/uc/lexer: Add benchmark.

As compared to Gocc, the regexp based lexer generated by genlex
is roughly two orders of magnitude slower.

examples/uc/lexer/lexer_test.go

@@ -0,0 +1,31 @@
+package lexer_test
+
+import (
+	"io"
+	"io/ioutil"
+	"testing"
+
+	"github.com/mewmew/speak/examples/uc/lexer"
+	"github.com/pkg/errors"
+)
+
+func BenchmarkLexerScan(b *testing.B) {
+	buf, err := ioutil.ReadFile("../testdata/input.c")
+	if err != nil {
+		b.Fatal(err)
+	}
+	b.ResetTimer()
+	b.SetBytes(int64(len(buf)))
+	for i := 0; i < b.N; i++ {
+		l := lexer.NewFromBytes(buf)
+		for {
+			_, err := l.Scan()
+			if err != nil {
+				if errors.Cause(err) == io.EOF {
+					break
+				}
+				b.Fatalf("lexer error; %v", err)
+			}
+		}
+	}
+}