feat: make Next iterator instruction faster and more efficient

Branching control is delegated directly to the Next instruction,
which now takes the location of loop exit as first argument.
It avoids the use of JumpFalse, plus the stack storage for the
condition.

1 files changed, 7 insertions, 6 deletions

diff --git a/vm/vm.go b/vm/vm.go
index f6dc6fc..7ab5a25 100644
--- a/vm/vm.go
+++ b/vm/vm.go
@@ -108,8 +108,8 @@ func (m *Machine) Run() (err error) {
 	defer func() { m.mem, m.ip, m.fp, m.ic = mem, ip, fp, ic }()
 
 	for {
-		sp = len(mem) // stack pointer
-		c := m.code[ip]
+		sp = len(mem)   // stack pointer
+		c := m.code[ip] // current instruction
 		if debug {
 			log.Printf("ip:%-3d sp:%-3d fp:%-3d op:[%-20v] mem:%v\n", ip, sp, fp, c, Vstring(mem))
 		}
@@ -247,11 +247,12 @@ func (m *Machine) Run() (err error) {
 		case Negate:
 			mem[sp-1] = ValueOf(-mem[sp-1].Int())
 		case Next:
-			v, ok := mem[sp-2].Interface().(func() (reflect.Value, bool))()
-			if ok {
-				mem[c.Arg[0]].Set(v)
+			if v, ok := mem[sp-2].Interface().(func() (reflect.Value, bool))(); ok {
+				mem[c.Arg[1]].Set(v)
+			} else {
+				ip += c.Arg[0]
+				continue
 			}
-			mem = append(mem, ValueOf(ok))
 		case Not:
 			mem[sp-1] = ValueOf(!mem[sp-1].Bool())
 		case Pop: