Merge pull request #72 from d5/compiledset

replacing values of the compiled script

docs/interoperability.md

@@ -70,12 +70,23 @@ func main() {
 
 	// retrieve value of 'a'
 	a := c.Get("a")
-	fmt.Println(a.Int())
+	fmt.Println(a.Int())           // prints "30"
+	
+	// re-run after replacing value of 'b'
+	if err := c.Set("b", 20); err != nil {
+		panic(err)
+	}
+	if err := c.Run(); err != nil {
+		panic(err)
+	}
+	fmt.Println(c.Get("a").Int())  // prints "40"
 }
 ```
 
 A variable `b` is defined by the user before compilation using [Script.Add](https://godoc.org/github.com/d5/tengo/script#Script.Add) function. Then a compiled bytecode `c` is used to execute the bytecode and get the value of global variables. In this example, the value of global variable `a` is read using [Compiled.Get](https://godoc.org/github.com/d5/tengo/script#Compiled.Get) function. See [documentation](https://godoc.org/github.com/d5/tengo/script#Variable) for the full list of variable value functions.
 
+Value of the global variables can be replaced using [Compiled.Set](https://godoc.org/github.com/d5/tengo/script#Compiled.Set) function. But it will return an error if you try to set the value of un-defined global variables _(e.g. trying to set the value of `x` in the example)_.  
+
 ### Type Conversion Table
 
 When adding a Variable _([Script.Add](https://godoc.org/github.com/d5/tengo/script#Script.Add))_, Script converts Go values into Tengo values based on the following conversion table.

runtime/vm.go

@@ -80,6 +80,15 @@ func (v *VM) Abort() {
 
 // Run starts the execution.
 func (v *VM) Run() error {
+	// reset VM states
+	v.sp = 0
+	v.curFrame = &(v.frames[0])
+	v.curInsts = v.curFrame.fn.Instructions
+	v.curIPLimit = len(v.curInsts) - 1
+	v.framesIndex = 1
+	v.ip = -1
+	atomic.StoreInt64(&v.aborting, 0)
+
 	for v.ip < v.curIPLimit && (atomic.LoadInt64(&v.aborting) == 0) {
 		v.ip++
 

script/compiled.go

@@ -2,6 +2,7 @@ package script
 
 import (
 	"context"
+	"fmt"
 
 	"github.com/d5/tengo/compiler"
 	"github.com/d5/tengo/objects"
@@ -92,3 +93,21 @@ func (c *Compiled) GetAll() []*Variable {
 
 	return vars
 }
+
+// Set replaces the value of a global variable identified by the name.
+// An error will be returned if the name was not defined during compilation.
+func (c *Compiled) Set(name string, value interface{}) error {
+	obj, err := objects.FromInterface(value)
+	if err != nil {
+		return err
+	}
+
+	symbol, _, ok := c.symbolTable.Resolve(name)
+	if !ok || symbol.Scope != compiler.ScopeGlobal {
+		return fmt.Errorf("'%s' is not defined", name)
+	}
+
+	c.machine.Globals()[symbol.Index] = &obj
+
+	return nil
+}

script/compiled_test.go

@@ -47,6 +47,36 @@ func TestCompiled_IsDefined(t *testing.T) {
 	compiledIsDefined(t, c, "b", false)
 }
 
+func TestCompiled_Set(t *testing.T) {
+	c := compile(t, `a := b`, M{"b": "foo"})
+	compiledRun(t, c)
+	compiledGet(t, c, "a", "foo")
+
+	// replace value of 'b'
+	err := c.Set("b", "bar")
+	assert.NoError(t, err)
+	compiledRun(t, c)
+	compiledGet(t, c, "a", "bar")
+
+	// try to replace undefined variable
+	err = c.Set("c", 1984)
+	assert.Error(t, err) // 'c' is not defined
+
+	// case #2
+	c = compile(t, `
+a := func() { 
+	return func() {
+		return b + 5
+	}() 
+}()`, M{"b": 5})
+	compiledRun(t, c)
+	compiledGet(t, c, "a", int64(10))
+	err = c.Set("b", 10)
+	assert.NoError(t, err)
+	compiledRun(t, c)
+	compiledGet(t, c, "a", int64(15))
+}
+
 func TestCompiled_RunContext(t *testing.T) {
 	// machine completes normally
 	c := compile(t, `a := 5`, nil)