reduce ssvWriter allocation in funcSort

mark             old ns/op     new ns/op     delta
BenchmarkFuncSort     1572          1413          -10.11%

benchmark             old allocs     new allocs     delta
BenchmarkFuncSort     8              7              -12.50%

benchmark             old bytes     new bytes     delta
benchmarkFuncSort     188           156           -17.02%

2 files changed, 26 insertions, 4 deletions

diff --git a/func.go b/func.go
index 550f67b..62e9af4 100644
--- a/func.go
+++ b/func.go
@@ -303,12 +303,15 @@ func (f *funcSort) Eval(w io.Writer, ev *Evaluator) {
 
 	// Remove duplicate words.
 	var prev string
-	sw := ssvWriter{w: w}
 	for _, tok := range toks {
-		if prev != tok {
-			sw.WriteString(tok)
-			prev = tok
+		if prev == tok {
+			continue
+		}
+		if prev != "" {
+			writeByte(w, ' ')
 		}
+		io.WriteString(w, tok)
+		prev = tok
 	}
 	addStats("funcbody", "sort", t)
 }
diff --git a/func_test.go b/func_test.go
index 07b00a0..7fae5f2 100644
--- a/func_test.go
+++ b/func_test.go
@@ -37,3 +37,22 @@ func BenchmarkFuncStrip(b *testing.B) {
 		strip.Eval(&buf, ev)
 	}
 }
+
+func BenchmarkFuncSort(b *testing.B) {
+	sort := &funcSort{
+		fclosure: fclosure{
+			args: []Value{
+				literal("(sort"),
+				literal("foo bar lose"),
+			},
+		},
+	}
+	ev := newEvaluator(make(map[string]Var))
+	var buf bytes.Buffer
+	b.ReportAllocs()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		buf.Reset()
+		sort.Eval(&buf, ev)
+	}
+}