allow to reuse vm

Author: antonmedv

bench_test.go

@@ -32,7 +32,7 @@ func debugger() {
 	program, err := compiler.Compile(tree, nil)
 	check(err)
 
-	vm := NewVM(true)
+	vm := Debug()
 
 	app := tview.NewApplication()
 	table := tview.NewTable()
@@ -54,7 +54,7 @@ func debugger() {
 	app.SetRoot(flex, true)
 
 	go func() {
-		out := vm.Run(program, nil)
+		out, _ := vm.Run(program, nil)
 		app.QueueUpdateDraw(func() {
 			sub.RemoveItem(scope)
 			result := tview.NewTextView()

cmd/exe/debugger.go

@@ -79,4 +79,41 @@ Will be replaced with result of `fib(42)` on compile step. No need to calculate
 
 [ConstExpr Example](https://pkg.go.dev/github.com/antonmedv/expr?tab=doc#ConstExpr)
 
+## Reuse VM
+
+It is possible to reuse a virtual machine between re-runs on the program. 
+This adds a small increase in performance (from 4% to 40% depending on a program).
+
+```go
+package main
+
+import (
+	"fmt"
+	"github.com/antonmedv/expr"
+	"github.com/antonmedv/expr/vm"
+)
+
+func main() {
+	env := map[string]interface{}{
+		"foo": 1,
+		"bar": 2,
+	}
+
+	program, err := expr.Compile("foo + bar", expr.Env(env))
+	if err != nil {
+		panic(err)
+	}
+
+	// Reuse this vm instance between runs
+	v := vm.VM{}
+
+	out, err := v.Run(program, env)
+	if err != nil {
+		panic(err)
+	}
+
+	fmt.Print(out)
+}
+```
+
 * [Contents](README.md)

docs/Optimizations.md

@@ -1,6 +1,8 @@
 github.com/DATA-DOG/go-sqlmock v1.3.3/go.mod h1:f/Ixk793poVmq4qj/V1dPUg2JEAKC73Q5eFN3EC/SaM=
 github.com/davecgh/go-spew v0.0.0-20161028175848-04cdfd42973b/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/gdamore/encoding v1.0.0 h1:+7OoQ1Bc6eTm5niUzBa0Ctsh6JbMW6Ra+YNuAtDBdko=
 github.com/gdamore/encoding v1.0.0/go.mod h1:alR0ol34c49FCSBLjhosxzcPHQbf2trDkoo5dl+VrEg=
 github.com/gdamore/tcell v1.3.0 h1:r35w0JBADPZCVQijYebl6YMWWtHRqVEGt7kL2eBADRM=
 github.com/gdamore/tcell v1.3.0/go.mod h1:Hjvr+Ofd+gLglo7RYKxxnzCBmev3BzsS67MebKS4zMM=
@@ -11,6 +13,7 @@ github.com/mattn/go-runewidth v0.0.4/go.mod h1:LwmH8dsx7+W8Uxz3IHJYH5QSwggIsqBzp
 github.com/mattn/go-runewidth v0.0.8 h1:3tS41NlGYSmhhe/8fhGRzc+z3AYCw1Fe1WAyLuujKs0=
 github.com/mattn/go-runewidth v0.0.8/go.mod h1:H031xJmbD/WCDINGzjvQ9THkh0rPKHF+m2gUSrubnMI=
 github.com/pmezard/go-difflib v0.0.0-20151028094244-d8ed2627bdf0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/rivo/tview v0.0.0-20200219210816-cd38d7432498 h1:4CFNy7/q7P06AsIONZzuWy7jcdqEmYQvOZ9FAFZdbls=
 github.com/rivo/tview v0.0.0-20200219210816-cd38d7432498/go.mod h1:6lkG1x+13OShEf0EaOCaTQYyB7d5nSbb181KtjlS+84=
@@ -26,7 +29,9 @@ golang.org/x/sys v0.0.0-20190626150813-e07cf5db2756/go.mod h1:h1NjWce9XRLGQEsW7w
 golang.org/x/sys v0.0.0-20200212091648-12a6c2dcc1e4 h1:sfkvUWPNGwSV+8/fNqctR5lS2AqCSqYwXdrjCxp/dXo=
 golang.org/x/sys v0.0.0-20200212091648-12a6c2dcc1e4/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+golang.org/x/text v0.3.2 h1:tW2bmiBqwgJj/UpqtC8EpXEZVYOwU0yG4iWbprSVAcs=
 golang.org/x/text v0.3.2/go.mod h1:bEr9sfX3Q8Zfm5fL9x+3itogRgK3+ptLWKqgva+5dAk=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v2 v2.2.2 h1:ZCJp+EgiOT7lHqUV2J862kp8Qj64Jo6az82+3Td9dZw=
 gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=

go.sum

@@ -13,25 +13,13 @@ var (
 	MemoryBudget int = 1e6
 )
 
-func Run(program *Program, env interface{}) (out interface{}, err error) {
+func Run(program *Program, env interface{}) (interface{}, error) {
 	if program == nil {
 		return nil, fmt.Errorf("program is nil")
 	}
 
-	vm := NewVM(false)
-
-	defer func() {
-		if r := recover(); r != nil {
-			f := &file.Error{
-				Location: program.Locations[vm.pp],
-				Message:  fmt.Sprintf("%v", r),
-			}
-			err = f.Bind(program.Source)
-		}
-	}()
-
-	out = vm.Run(program, env)
-	return
+	vm := VM{}
+	return vm.Run(program, env)
 }
 
 type VM struct {
@@ -48,20 +36,40 @@ type VM struct {
 	limit     int
 }
 
-func NewVM(debug bool) *VM {
+func Debug() *VM {
 	vm := &VM{
-		stack: make([]interface{}, 0, 2),
-		debug: debug,
-		limit: MemoryBudget,
-	}
-	if vm.debug {
-		vm.step = make(chan struct{}, 0)
-		vm.curr = make(chan int, 0)
+		debug: true,
+		step:  make(chan struct{}, 0),
+		curr:  make(chan int, 0),
 	}
 	return vm
 }
 
-func (vm *VM) Run(program *Program, env interface{}) interface{} {
+func (vm *VM) Run(program *Program, env interface{}) (out interface{}, err error) {
+	defer func() {
+		if r := recover(); r != nil {
+			f := &file.Error{
+				Location: program.Locations[vm.pp],
+				Message:  fmt.Sprintf("%v", r),
+			}
+			err = f.Bind(program.Source)
+		}
+	}()
+
+	vm.limit = MemoryBudget
+	vm.ip = 0
+	vm.pp = 0
+
+	if vm.stack == nil {
+		vm.stack = make([]interface{}, 0, 2)
+	} else {
+		vm.stack = vm.stack[0:0]
+	}
+
+	if vm.scopes != nil {
+		vm.scopes = vm.scopes[0:0]
+	}
+
 	vm.bytecode = program.Bytecode
 	vm.constants = program.Constants
 
@@ -379,10 +387,10 @@ func (vm *VM) Run(program *Program, env interface{}) interface{} {
 	}
 
 	if len(vm.stack) > 0 {
-		return vm.pop()
+		return vm.pop(), nil
 	}
 
-	return nil
+	return nil, nil
 }
 
 func (vm *VM) push(value interface{}) {