vm: Add basic support for VM instances to be reused (via Reset())

[deanm]

Adds a bench mark that shows this something around a 30% difference.

Benchmark_NewVMs-4 3000000 431 ns/op
Benchmark_ReuseVMs-4 5000000 302 ns/op

[ghost]

I would suggest removing the Reset method and simply place it at the beginning of the Run call:

diff --git a/bench_test.go b/bench_test.go
index 61c6e55..82dd247 100644
--- a/bench_test.go
+++ b/bench_test.go
@@ -202,7 +202,6 @@ func Benchmark_ReuseVMs(b *testing.B) {
 	v := vm.NewVM(false)
 
 	for n := 0; n < b.N; n++ {
-		v.Reset()
 		_, err = v.RunSafe(program, &env)
 	}
 
diff --git a/vm/vm.go b/vm/vm.go
index 704c42c..90b6257 100644
--- a/vm/vm.go
+++ b/vm/vm.go
@@ -53,18 +53,16 @@ func (vm *VM) RunSafe(program *Program, env interface{}) (out interface{}, err e
 	return
 }
 
-func (vm *VM) Reset() {
+func (vm *VM) Run(program *Program, env interface{}) interface{} {
+
 	vm.stack = vm.stack[0:0] // keep the existing memory/capacity
+	vm.bytecode = program.Bytecode
+	vm.constants = program.Constants
 	vm.ip = 0
 	vm.pp = 0
 	if vm.scopes != nil {
 		vm.scopes = vm.scopes[0:0] // keep the existing memory/capacity
 	}
-}
-
-func (vm *VM) Run(program *Program, env interface{}) interface{} {
-	vm.bytecode = program.Bytecode
-	vm.constants = program.Constants
 
 	for vm.ip < len(vm.bytecode) {

[antonmedv]

Closed as of #107