diff --git a/VERSION b/VERSION
index bb22182d4..4ef2eb086 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-0.38.1
+0.39.0
diff --git a/pkg/vm/README.md b/pkg/vm/README.md
index fc7a12230..76b440f33 100644
--- a/pkg/vm/README.md
+++ b/pkg/vm/README.md
@@ -52,27 +52,29 @@ More information about standalone installation coming soon.
 NEO-GO-VM > help
 
 COMMAND    USAGE
-step       step (n) instruction in the program (> step 10)
-ops        show the opcodes of the current loaded program
-ip         show the current instruction
-estack     show evaluation stack details
 astack     show alt stack details
-istack     show invocation stack details
-run        execute the current loaded script
-cont       continue execution of the current loaded script
-help       show available commands
-exit       exit the VM prompt
 break      place a breakpoint (> break 1)
-load       load a script into the VM (> load /path/to/script.avm)
+cont       continue execution of the current loaded script
+estack     show evaluation stack details
+exit       exit the VM prompt
+help       show available commands
+ip         show the current instruction
+istack     show invocation stack details
+loadavm    load an avm script into the VM (> load /path/to/script.avm)
+loadgo     compile and load a .go file into the VM (> load /path/to/file.go)
+loadhex    load a hex string into the VM (> loadhex 006166 )
+ops        show the opcodes of the current loaded program
+run        execute the current loaded script
+step       step (n) instruction in the program (> step 10)
 ```
 
 ### Loading in your script
 
-To load a script into the VM:
+To load an avm script into the VM:
 
 ```
-NEO-GO-VM > load ../contract.avm
-READY
+NEO-GO-VM > loadavm ../contract.avm
+READY: loaded 36 instructions
 ```
 
 Run the script:
@@ -87,6 +89,28 @@ NEO-GO-VM > run
 ]
 ```
 
+You can also directly compile and load `.go` files:
+
+```
+NEO-GO-VM > loadgo ../contract.go
+READY: loaded 36 instructions
+```
+
+To make it even more complete, you can directly load hex strings into the VM:
+
+```
+NEO-GO-VM > loadhex 54c56b006c766b00527ac46c766b00c391640b006203005a616c756662030000616c7566
+READY: loaded 36 instructions
+NEO-GO-VM > run
+[
+    {
+        "value": 10,
+        "type": "BigInteger"
+    }
+]
+
+```
+
 ### Debugging
 The `neo-go-vm` provides a debugger to inspect your program in-depth.
 
@@ -95,6 +119,7 @@ Step 4 instructions.
 ```
 NEO-GO-VM > step 4
 at breakpoint 4 (Opush4)
+NEO-GO-VM 4 >
 ```
 
 Using just `step` will execute 1 instruction at a time.
@@ -102,6 +127,7 @@ Using just `step` will execute 1 instruction at a time.
 ```
 NEO-GO-VM > step
 instruction pointer at 5 (Odup)
+NEO-GO-VM 5 >
 ```
 
 To place breakpoints:
@@ -109,14 +135,15 @@ To place breakpoints:
 ```
 NEO-GO-VM > break 10
 breakpoint added at instruction 10
-NEO-GO-VM > resume
+NEO-GO-VM > cont
 at breakpoint 10 (Osetitem)
+NEO-GO-VM 10 > cont
 ```
 
-Inspecting the stack:
+Inspecting the evaluation stack:
 
 ```
-NEO-GO-VM > stack
+NEO-GO-VM > estack
 [
     {
         "value": [
@@ -137,4 +164,7 @@ NEO-GO-VM > stack
 ]
 ```
 
-And a lot more features coming next weeks..
+There are more stacks that you can inspect.
+- `astack` alt stack
+- `istack` invocation stack
+
diff --git a/pkg/vm/cli/cli.go b/pkg/vm/cli/cli.go
index 0063d5eaf..782adf5ed 100644
--- a/pkg/vm/cli/cli.go
+++ b/pkg/vm/cli/cli.go
@@ -2,40 +2,45 @@ package cli
 
 import (
 	"bufio"
+	"bytes"
+	"encoding/hex"
 	"fmt"
+	"io/ioutil"
 	"os"
+	"sort"
 	"strconv"
 	"strings"
 	"text/tabwriter"
 
 	"github.com/CityOfZion/neo-go/pkg/vm"
+	"github.com/CityOfZion/neo-go/pkg/vm/compiler"
 )
 
 // command describes a VM command.
 type command struct {
 	// number of minimun arguments the command needs.
 	args int
-
 	// description of the command.
 	usage string
-
 	// whether the VM needs to be "ready" to execute this command.
 	ready bool
 }
 
 var commands = map[string]command{
-	"help":   {0, "show available commands", false},
-	"exit":   {0, "exit the VM prompt", false},
-	"ip":     {0, "show the current instruction", true},
-	"break":  {1, "place a breakpoint (> break 1)", true},
-	"estack": {0, "show evaluation stack details", false},
-	"astack": {0, "show alt stack details", false},
-	"istack": {0, "show invocation stack details", false},
-	"load":   {1, "load a script into the VM (> load /path/to/script.avm)", false},
-	"run":    {0, "execute the current loaded script", true},
-	"cont":   {0, "continue execution of the current loaded script", true},
-	"step":   {0, "step (n) instruction in the program (> step 10)", true},
-	"ops":    {0, "show the opcodes of the current loaded program", true},
+	"help":    {0, "show available commands", false},
+	"exit":    {0, "exit the VM prompt", false},
+	"ip":      {0, "show the current instruction", true},
+	"break":   {1, "place a breakpoint (> break 1)", true},
+	"estack":  {0, "show evaluation stack details", false},
+	"astack":  {0, "show alt stack details", false},
+	"istack":  {0, "show invocation stack details", false},
+	"loadavm": {1, "load an avm script into the VM (> load /path/to/script.avm)", false},
+	"loadhex": {1, "load a hex string into the VM (> loadhex 006166 )", false},
+	"loadgo":  {1, "compile and load a .go file into the VM (> load /path/to/file.go)", false},
+	"run":     {0, "execute the current loaded script", true},
+	"cont":    {0, "continue execution of the current loaded script", true},
+	"step":    {0, "step (n) instruction in the program (> step 10)", true},
+	"ops":     {0, "show the opcodes of the current loaded program", true},
 }
 
 // VMCLI object for interacting with the VM.
@@ -67,14 +72,7 @@ func (c *VMCLI) handleCommand(cmd string, args ...string) {
 
 	switch cmd {
 	case "help":
-		fmt.Println()
-		w := tabwriter.NewWriter(os.Stdout, 0, 0, 4, ' ', 0)
-		fmt.Fprintln(w, "COMMAND\tUSAGE")
-		for name, details := range commands {
-			fmt.Fprintf(w, "%s\t%s\n", name, details.usage)
-		}
-		w.Flush()
-		fmt.Println()
+		printHelp()
 
 	case "exit":
 		fmt.Println("Bye!")
@@ -97,13 +95,36 @@ func (c *VMCLI) handleCommand(cmd string, args ...string) {
 	case "estack", "istack", "astack":
 		fmt.Println(c.vm.Stack(cmd))
 
-	case "load":
+	case "loadavm":
 		if err := c.vm.LoadFile(args[0]); err != nil {
 			fmt.Println(err)
 		} else {
 			fmt.Printf("READY: loaded %d instructions\n", c.vm.Context().LenInstr())
 		}
 
+	case "loadhex":
+		b, err := hex.DecodeString(args[0])
+		if err != nil {
+			fmt.Println(err)
+			return
+		}
+		c.vm.Load(b)
+		fmt.Printf("READY: loaded %d instructions\n", c.vm.Context().LenInstr())
+
+	case "loadgo":
+		fb, err := ioutil.ReadFile(args[0])
+		if err != nil {
+			fmt.Println(err)
+			return
+		}
+		b, err := compiler.Compile(bytes.NewReader(fb), &compiler.Options{})
+		if err != nil {
+			fmt.Println(err)
+			return
+		}
+		c.vm.Load(b)
+		fmt.Printf("READY: loaded %d instructions\n", c.vm.Context().LenInstr())
+
 	case "run", "cont":
 		c.vm.Run()
 
@@ -132,7 +153,11 @@ func (c *VMCLI) Run() error {
 	printLogo()
 	reader := bufio.NewReader(os.Stdin)
 	for {
-		fmt.Print("NEO-GO-VM > ")
+		if c.vm.Ready() && c.vm.Context().IP()-1 >= 0 {
+			fmt.Printf("NEO-GO-VM %d > ", c.vm.Context().IP()-1)
+		} else {
+			fmt.Print("NEO-GO-VM > ")
+		}
 		input, _ := reader.ReadString('\n')
 		input = strings.Trim(input, "\n")
 		if len(input) != 0 {
@@ -147,6 +172,25 @@ func (c *VMCLI) Run() error {
 	}
 }
 
+func printHelp() {
+	names := make([]string, len(commands))
+	i := 0
+	for name, _ := range commands {
+		names[i] = name
+		i++
+	}
+	sort.Strings(names)
+
+	fmt.Println()
+	w := tabwriter.NewWriter(os.Stdout, 0, 0, 4, ' ', 0)
+	fmt.Fprintln(w, "COMMAND\tUSAGE")
+	for _, name := range names {
+		fmt.Fprintf(w, "%s\t%s\n", name, commands[name].usage)
+	}
+	w.Flush()
+	fmt.Println()
+}
+
 func printLogo() {
 	logo := `
     _   ____________        __________      _    ____  ___
diff --git a/pkg/vm/compiler/README.md b/pkg/vm/compiler/README.md
index 6cd0456c3..fac47a5a7 100644
--- a/pkg/vm/compiler/README.md
+++ b/pkg/vm/compiler/README.md
@@ -15,19 +15,19 @@ The neo-go compiler compiles Go programs to bytecode that the NEO virtual machin
 - basic if statements
 - binary expressions
 - return statements
+- for loops
 - imports 
 
 ### Go builtins
 - len
+- append
 
 ### VM API (interop layer)
 - storage
 - runtime
 
 ## Not yet implemented
-- for loops
 - range
-- builtin (append)
 - some parts of the interop layer (VM API)
 
 ## Not supported
diff --git a/pkg/vm/compiler/analysis.go b/pkg/vm/compiler/analysis.go
index f9ee20179..85a267e61 100644
--- a/pkg/vm/compiler/analysis.go
+++ b/pkg/vm/compiler/analysis.go
@@ -192,3 +192,7 @@ func isNoRetSyscall(name string) bool {
 	}
 	return false
 }
+
+func isStringType(t types.Type) bool {
+	return t.String() == "string"
+}
diff --git a/pkg/vm/compiler/codegen.go b/pkg/vm/compiler/codegen.go
index bc4285b88..49b0e91c2 100644
--- a/pkg/vm/compiler/codegen.go
+++ b/pkg/vm/compiler/codegen.go
@@ -380,15 +380,16 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
 
 	case *ast.CallExpr:
 		var (
-			f       *funcScope
-			ok      bool
-			numArgs = len(n.Args)
+			f         *funcScope
+			ok        bool
+			numArgs   = len(n.Args)
+			isBuiltin = isBuiltin(n.Fun)
 		)
 
 		switch fun := n.Fun.(type) {
 		case *ast.Ident:
 			f, ok = c.funcs[fun.Name]
-			if !ok && !isBuiltin(n.Fun) {
+			if !ok && !isBuiltin {
 				log.Fatalf("could not resolve function %s", fun.Name)
 			}
 		case *ast.SelectorExpr:
@@ -410,12 +411,15 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
 		for _, arg := range n.Args {
 			ast.Walk(c, arg)
 		}
-		if numArgs == 2 {
-			emitOpcode(c.prog, vm.Oswap)
-		}
-		if numArgs == 3 {
-			emitInt(c.prog, 2)
-			emitOpcode(c.prog, vm.Oxswap)
+		// Do not swap for builtin functions.
+		if !isBuiltin {
+			if numArgs == 2 {
+				emitOpcode(c.prog, vm.Oswap)
+			}
+			if numArgs == 3 {
+				emitInt(c.prog, 2)
+				emitOpcode(c.prog, vm.Oxswap)
+			}
 		}
 
 		// c# compiler adds a NOP (0x61) before every function call. Dont think its relevant
@@ -424,7 +428,7 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
 		emitOpcode(c.prog, vm.Onop)
 
 		// Check builtin first to avoid nil pointer on funcScope!
-		if isBuiltin(n.Fun) {
+		if isBuiltin {
 			// Use the ident to check, builtins are not in func scopes.
 			// We can be sure builtins are of type *ast.Ident.
 			c.convertBuiltin(n.Fun.(*ast.Ident).Name, n)
@@ -456,7 +460,9 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
 		return nil
 
 	case *ast.UnaryExpr:
-		// TODO(@anthdm)
+		ast.Walk(c, n.X)
+		c.convertToken(n.Op)
+		return nil
 
 	case *ast.IncDecStmt:
 		ast.Walk(c, n.X)
@@ -528,9 +534,15 @@ func (c *codegen) convertSyscall(name string) {
 func (c *codegen) convertBuiltin(name string, expr *ast.CallExpr) {
 	switch name {
 	case "len":
-		emitOpcode(c.prog, vm.Oarraysize)
+		arg := expr.Args[0]
+		typ := c.typeInfo.Types[arg].Type
+		if isStringType(typ) {
+			emitOpcode(c.prog, vm.Osize)
+		} else {
+			emitOpcode(c.prog, vm.Oarraysize)
+		}
 	case "append":
-		log.Fatal("builtin (append) not yet implemented.")
+		emitOpcode(c.prog, vm.Oappend)
 	}
 }
 
@@ -621,6 +633,8 @@ func (c *codegen) convertToken(tok token.Token) {
 		emitOpcode(c.prog, vm.Odec)
 	case token.INC:
 		emitOpcode(c.prog, vm.Oinc)
+	case token.NOT:
+		emitOpcode(c.prog, vm.Onot)
 	default:
 		log.Fatalf("compiler could not convert token: %s", tok)
 	}
@@ -702,7 +716,7 @@ func (c *codegen) writeJumps() {
 		switch vm.Opcode(op) {
 		case vm.Ojmp, vm.Ojmpifnot, vm.Ojmpif, vm.Ocall:
 			index := int16(binary.LittleEndian.Uint16(b[j : j+2]))
-			if int(index) > len(c.l) {
+			if int(index) > len(c.l) || int(index) < 0 {
 				continue
 			}
 			offset := uint16(c.l[index] - i)
diff --git a/pkg/vm/compiler/tests/bool_test.go b/pkg/vm/compiler/tests/bool_test.go
deleted file mode 100644
index 5a59c9d16..000000000
--- a/pkg/vm/compiler/tests/bool_test.go
+++ /dev/null
@@ -1,57 +0,0 @@
-package compiler
-
-var boolTestCases = []testCase{
-	{
-		"bool assign",
-		`
-		package foo
-		func Main() bool {
-			x := true
-			return x
-		}
-		`,
-		"52c56b516c766b00527ac46203006c766b00c3616c7566",
-	},
-	{
-		"bool compare",
-		`
-		package foo
-		func Main() int {
-			x := true
-			if x {
-				return 10
-			}
-			return 0
-		}
-		`,
-		"54c56b516c766b00527ac46c766b00c3640b006203005a616c756662030000616c7566",
-	},
-	{
-		"bool compare verbose",
-		`
-		package foo
-		func Main() int {
-			x := true
-			if x == true {
-				return 10
-			}
-			return 0
-		}
-		`,
-		"54c56b516c766b00527ac46c766b00c3519c640b006203005a616c756662030000616c7566",
-	},
-	//	{
-	//		"bool invert (unary expr)",
-	//		`
-	//		package foo
-	//		func Main() int {
-	//			x := true
-	//			if !x {
-	//				return 10
-	//			}
-	//			return 0
-	//		}
-	//		`,
-	//		"54c56b516c766b00527ac46c766b00c3630b006203005a616c756662030000616c7566",
-	//	},
-}
diff --git a/pkg/vm/compiler/tests/string_test.go b/pkg/vm/compiler/tests/string_test.go
deleted file mode 100644
index 284b87c9f..000000000
--- a/pkg/vm/compiler/tests/string_test.go
+++ /dev/null
@@ -1,15 +0,0 @@
-package compiler
-
-var stringTestCases = []testCase{
-	{
-		"simple string",
-		`
-		package testcase
-		func Main() string {
-			x := "NEO"
-			return x
-		}
-		`,
-		"52c56b034e454f6c766b00527ac46203006c766b00c3616c7566",
-	},
-}
diff --git a/pkg/vm/context.go b/pkg/vm/context.go
index 3c56904b9..ed4fef036 100644
--- a/pkg/vm/context.go
+++ b/pkg/vm/context.go
@@ -28,10 +28,13 @@ func NewContext(b []byte) *Context {
 // Next return the next instruction to execute.
 func (c *Context) Next() Opcode {
 	c.ip++
+	if c.ip >= len(c.prog) {
+		return Oret
+	}
 	return Opcode(c.prog[c.ip])
 }
 
-// IP returns the absosulute instruction without taking 0 into account.
+// IP returns the absolute instruction without taking 0 into account.
 // If that program starts the ip = 0 but IP() will return 1, cause its
 // the first instruction.
 func (c *Context) IP() int {
diff --git a/pkg/vm/stack.go b/pkg/vm/stack.go
index 7b6d05559..80d139324 100644
--- a/pkg/vm/stack.go
+++ b/pkg/vm/stack.go
@@ -72,6 +72,9 @@ func (e *Element) BigInt() *big.Int {
 // Bool attempts to get the underlying value of the element as a boolean.
 // Will panic if the assertion failed which will be catched by the VM.
 func (e *Element) Bool() bool {
+	if v, ok := e.value.Value().(*big.Int); ok {
+		return v.Int64() == 1
+	}
 	return e.value.Value().(bool)
 }
 
diff --git a/pkg/vm/test/array_test.go b/pkg/vm/test/array_test.go
deleted file mode 100644
index 0c36e39cf..000000000
--- a/pkg/vm/test/array_test.go
+++ /dev/null
@@ -1,117 +0,0 @@
-package vm_test
-
-import (
-	"math/big"
-
-	"github.com/CityOfZion/neo-go/pkg/vm"
-)
-
-var arrayTestCases = []testCase{
-	{
-		"assign int array",
-		`
-		package foo
-		func Main() []int {
-			x := []int{1, 2, 3}
-			return x
-		}
-		`,
-		[]vm.StackItem{
-			vm.NewBigIntegerItem(1),
-			vm.NewBigIntegerItem(2),
-			vm.NewBigIntegerItem(3),
-		},
-	},
-	{
-		"assign string array",
-		`
-		package foo
-		func Main() []string {
-			x := []string{"foo", "bar", "foobar"}
-			return x
-		}
-		`,
-		[]vm.StackItem{
-			vm.NewByteArrayItem([]byte("foo")),
-			vm.NewByteArrayItem([]byte("bar")),
-			vm.NewByteArrayItem([]byte("foobar")),
-		},
-	},
-	{
-		"array item assign",
-		`
-		package foo
-		func Main() int {
-			x := []int{0, 1, 2}
-			y := x[0]
-			return y
-		}
-		`,
-		big.NewInt(0),
-	},
-	{
-		"array item return",
-		`
-		package foo
-		func Main() int {
-			x := []int{0, 1, 2}
-			return x[1]
-		}
-		`,
-		big.NewInt(1),
-	},
-	{
-		"array item in bin expr",
-		`
-		package foo
-		func Main() int {
-			x := []int{0, 1, 2}
-			return x[1] + 10
-		}
-		`,
-		big.NewInt(11),
-	},
-	{
-		"array item ident",
-		`
-		package foo
-		func Main() int {
-			x := 1
-			y := []int{0, 1, 2}
-			return y[x]
-		}
-		`,
-		big.NewInt(1),
-	},
-	{
-		"array item index with binExpr",
-		`
-		package foo
-		func Main() int {
-			x := 1
-			y := []int{0, 1, 2}
-			return y[x + 1]
-		}
-		`,
-		big.NewInt(2),
-	},
-	{
-		"array item struct",
-		`
-		package foo
-
-		type Bar struct {
-			arr []int
-		}
-
-		func Main() int {
-			b := Bar{
-				arr: []int{0, 1, 2},
-			}
-			x := b.arr[2]
-			return x + 2
-		}
-		`,
-		big.NewInt(4),
-	},
-}
diff --git a/pkg/vm/test/for_test.go b/pkg/vm/test/for_test.go
deleted file mode 100644
index ac0b16234..000000000
--- a/pkg/vm/test/for_test.go
+++ /dev/null
@@ -1,36 +0,0 @@
-package vm_test
-
-import (
-	"math/big"
-	"testing"
-)
-
-func TestClassicForLoop(t *testing.T) {
-	src := `
-	package foo
-		func Main() int {
-			x := 0
-			for i := 0; i < 10; i++ {
-				x = i
-			}
-			return x
-		}
-	`
-	eval(t, src, big.NewInt(9))
-}
-
-// TODO: This could be a nasty bug. Output of the VM is 65695.
-// Only happens above 100000, could be binary read issue.
-//func TestForLoopBigIter(t *testing.T) {
-//	src := `
-//	package foo
-//		func Main() int {
-//			x := 0
-//			for i := 0; i < 100000; i++ {
-//				x = i
-//			}
-//			return x
-//		}
-//	`
-//	eval(t, src, big.NewInt(99999))
-//}
diff --git a/pkg/vm/test/assign_test.go b/pkg/vm/tests/assign_test.go
similarity index 100%
rename from pkg/vm/test/assign_test.go
rename to pkg/vm/tests/assign_test.go
diff --git a/pkg/vm/test/binary_expr_test.go b/pkg/vm/tests/binary_expr_test.go
similarity index 100%
rename from pkg/vm/test/binary_expr_test.go
rename to pkg/vm/tests/binary_expr_test.go
diff --git a/pkg/vm/tests/for_test.go b/pkg/vm/tests/for_test.go
new file mode 100644
index 000000000..1e17b3d5a
--- /dev/null
+++ b/pkg/vm/tests/for_test.go
@@ -0,0 +1,306 @@
+package vm_test
+
+import (
+	"math/big"
+	"testing"
+
+	"github.com/CityOfZion/neo-go/pkg/vm"
+)
+
+func TestArrayFieldInStruct(t *testing.T) {
+	src := `
+		package foo
+
+		type Bar struct {
+			arr []int
+		}
+
+		func Main() int {
+			b := Bar{
+				arr: []int{0, 1, 2},
+			}
+			x := b.arr[2]
+			return x + 2
+		}
+	`
+	eval(t, src, big.NewInt(4))
+}
+
+func TestArrayItemGetIndexBinaryExpr(t *testing.T) {
+	src := `
+		package foo
+		func Main() int {
+			x := 1
+			y := []int{0, 1, 2}
+			return y[x + 1]
+		}
+	`
+	eval(t, src, big.NewInt(2))
+}
+
+func TestArrayItemGetIndexIdent(t *testing.T) {
+	src := `
+		package foo
+		func Main() int {
+			x := 1
+			y := []int{0, 1, 2}
+			return y[x]
+		}
+	`
+	eval(t, src, big.NewInt(1))
+}
+
+func TestArrayItemBinExpr(t *testing.T) {
+	src := `
+		package foo
+		func Main() int {
+			x := []int{0, 1, 2}
+			return x[1] + 10
+		}
+	`
+	eval(t, src, big.NewInt(11))
+}
+
+func TestArrayItemReturn(t *testing.T) {
+	src := `
+		package foo
+		func Main() int {
+			arr := []int{0, 1, 2}
+			return arr[1]
+		}
+	`
+	eval(t, src, big.NewInt(1))
+}
+
+func TestArrayItemAssign(t *testing.T) {
+	src := `
+		package foo
+		func Main() int {
+			arr := []int{1, 2, 3}
+			y := arr[0]
+			return y
+		}
+	`
+	eval(t, src, big.NewInt(1))
+}
+
+func TestStringArray(t *testing.T) {
+	src := `
+		package foo
+		func Main() []string {
+			x := []string{"foo", "bar", "foobar"}
+			return x
+		}
+	`
+	eval(t, src, []vm.StackItem{
+		vm.NewByteArrayItem([]byte("foo")),
+		vm.NewByteArrayItem([]byte("bar")),
+		vm.NewByteArrayItem([]byte("foobar")),
+	})
+}
+
+func TestIntArray(t *testing.T) {
+	src := `
+		package foo
+		func Main() []int {
+			arr := []int{1, 2, 3}
+			return arr
+		}
+	`
+	eval(t, src, []vm.StackItem{
+		vm.NewBigIntegerItem(1),
+		vm.NewBigIntegerItem(2),
+		vm.NewBigIntegerItem(3),
+	})
+}
+
+func TestArrayLen(t *testing.T) {
+	src := `
+		package foo
+		func Main() int {
+			arr := []int{0, 1, 2}
+			return len(arr)
+		}
+	`
+	eval(t, src, big.NewInt(3))
+}
+
+func TestStringLen(t *testing.T) {
+	src := `
+		package foo
+		func Main() int {
+			str := "this is medium sized string"
+			return len(str)
+		}
+	`
+	eval(t, src, big.NewInt(27))
+}
+
+func TestSimpleString(t *testing.T) {
+	src := `
+		package foo
+		func Main() string {
+			x := "NEO"
+			return x
+		}
+	`
+	eval(t, src, vm.NewByteArrayItem([]byte("NEO")).Value())
+}
+
+func TestBoolAssign(t *testing.T) {
+	src := `
+		package foo
+		func Main() bool {
+			x := true
+			return x
+		}
+	`
+	eval(t, src, big.NewInt(1))
+}
+
+func TestBoolCompare(t *testing.T) {
+	src := `
+		package foo
+		func Main() int {
+			x := true
+			if x {
+				return 10
+			}
+			return 0
+		}
+	`
+	eval(t, src, big.NewInt(10))
+}
+
+func TestBoolCompareVerbose(t *testing.T) {
+	src := `
+		package foo
+		func Main() int {
+			x := true
+			if x == true {
+				return 10
+			}
+			return 0
+		}
+	`
+	eval(t, src, big.NewInt(10))
+}
+
+func TestUnaryExpr(t *testing.T) {
+	src := `
+		package foo
+		func Main() bool {
+			x := false
+			return !x
+		}
+	`
+	eval(t, src, true)
+}
+
+func TestIfUnaryInvertPass(t *testing.T) {
+	src := `
+		package foo
+		func Main() int {
+			x := false
+			if !x { 
+				return 10
+			}
+			return 0
+		}
+	`
+	eval(t, src, big.NewInt(10))
+}
+
+func TestIfUnaryInvert(t *testing.T) {
+	src := `
+		package foo
+		func Main() int {
+			x := true
+			if !x { 
+				return 10
+			}
+			return 0
+		}
+	`
+	eval(t, src, big.NewInt(0))
+}
+
+func TestAppendString(t *testing.T) {
+	src := `
+	package foo
+		func Main() string {
+			arr := []string{"a", "b", "c"}
+			arr = append(arr, "d")
+			return arr[3]
+		}
+	`
+	eval(t, src, vm.NewByteArrayItem([]byte("d")).Value())
+}
+
+func TestAppendInt(t *testing.T) {
+	src := `
+	package foo
+		func Main() int {
+			arr := []int{0, 1, 2}
+			arr = append(arr, 3)
+			return arr[3]
+		}
+	`
+	eval(t, src, big.NewInt(3))
+}
+
+func TestClassicForLoop(t *testing.T) {
+	src := `
+	package foo
+		func Main() int {
+			x := 0
+			for i := 0; i < 10; i++ {
+				x = i
+			}
+			return x
+		}
+	`
+	eval(t, src, big.NewInt(9))
+}
+
+func TestInc(t *testing.T) {
+	src := `
+	package foo
+		func Main() int {
+			x := 0
+			x++
+			return x
+		}
+	`
+
+	eval(t, src, big.NewInt(1))
+}
+
+func TestDec(t *testing.T) {
+	src := `
+	package foo
+		func Main() int {
+			x := 2
+			x--
+			return x
+		}
+	`
+
+	eval(t, src, big.NewInt(1))
+}
+
+// TODO: This could be a nasty bug. Output of the VM is 65695.
+// Only happens above 100000, could be binary read issue.
+//func TestForLoopBigIter(t *testing.T) {
+//	src := `
+//	package foo
+//		func Main() int {
+//			x := 0
+//			for i := 0; i < 100000; i++ {
+//				x = i
+//			}
+//			return x
+//		}
+//	`
+//	eval(t, src, big.NewInt(99999))
+//}
diff --git a/pkg/vm/test/numeric_test.go b/pkg/vm/tests/numeric_test.go
similarity index 100%
rename from pkg/vm/test/numeric_test.go
rename to pkg/vm/tests/numeric_test.go
diff --git a/pkg/vm/test/struct_test.go b/pkg/vm/tests/struct_test.go
similarity index 100%
rename from pkg/vm/test/struct_test.go
rename to pkg/vm/tests/struct_test.go
diff --git a/pkg/vm/test/vm_test.go b/pkg/vm/tests/vm_test.go
similarity index 95%
rename from pkg/vm/test/vm_test.go
rename to pkg/vm/tests/vm_test.go
index d0a8e9b9b..f533578a6 100644
--- a/pkg/vm/test/vm_test.go
+++ b/pkg/vm/tests/vm_test.go
@@ -33,7 +33,6 @@ func TestVMAndCompilerCases(t *testing.T) {
 	testCases := []testCase{}
 	testCases = append(testCases, numericTestCases...)
 	testCases = append(testCases, assignTestCases...)
-	testCases = append(testCases, arrayTestCases...)
 	testCases = append(testCases, binaryExprTestCases...)
 	testCases = append(testCases, structTestCases...)
 
diff --git a/pkg/vm/vm.go b/pkg/vm/vm.go
index fbb3149b9..fa197a323 100644
--- a/pkg/vm/vm.go
+++ b/pkg/vm/vm.go
@@ -186,10 +186,6 @@ func (v *VM) Run() {
 func (v *VM) Step() {
 	ctx := v.Context()
 	op := ctx.Next()
-	if ctx.ip >= len(ctx.prog) {
-		op = Oret
-	}
-
 	v.execute(ctx, op)
 
 	// re-peek the context as it could been changed during execution.
@@ -460,8 +456,8 @@ func (v *VM) execute(ctx *Context, op Opcode) {
 		v.estack.PushVal(x.Abs(x))
 
 	case Onot:
-		x := v.estack.Pop().BigInt()
-		v.estack.PushVal(x.Not(x))
+		x := v.estack.Pop().Bool()
+		v.estack.PushVal(!x)
 
 	case Onz:
 		panic("todo NZ")
@@ -486,6 +482,7 @@ func (v *VM) execute(ctx *Context, op Opcode) {
 		case *ArrayItem, *StructItem:
 			arr := t.Value().([]StackItem)
 			arr = append(arr, itemElem.value)
+			v.estack.PushVal(arr)
 		default:
 			panic("APPEND: not of underlying type Array")
 		}
@@ -558,6 +555,14 @@ func (v *VM) execute(ctx *Context, op Opcode) {
 		}
 		v.estack.PushVal(len(arr))
 
+	case Osize:
+		elem := v.estack.Pop()
+		arr, ok := elem.value.Value().([]uint8)
+		if !ok {
+			panic("SIZE: item not of type []uint8")
+		}
+		v.estack.PushVal(len(arr))
+
 	case Ojmp, Ojmpif, Ojmpifnot:
 		var (
 			rOffset = int16(ctx.readUint16())