use sync.Pool for temporal bytes.Buffer.

remove ev.Value and ev.Values

before:
 scanblock: 8.22s (14.83%)
 runtime.MScan_Sweep 4.99s(9.00%)

after:
 scanblock: 7.42s (12.95%)
 runtime.MScan_Sweep 4.57s(7.98%)

1 files changed, 4 insertions, 1 deletions

diff --git a/worker.go b/worker.go
index 456cf3d..5d3472f 100644
--- a/worker.go
+++ b/worker.go
@@ -113,7 +113,10 @@ func evalCmd(ev *Evaluator, r runner, s string) []runner {
 	if err != nil {
 		panic(fmt.Errorf("parse cmd %q: %v", r.cmd, err))
 	}
-	cmds := string(ev.Value(expr))
+	buf := newBuf()
+	expr.Eval(buf, ev)
+	cmds := buf.String()
+	freeBuf(buf)
 	var runners []runner
 	for _, cmd := range strings.Split(cmds, "\n") {
 		if len(runners) > 0 && strings.HasSuffix(runners[len(runners)-1].cmd, "\\") {