15 files changed, 374 insertions, 93 deletions

diff --git a/pkg/lang/vm/code/op.go b/pkg/lang/vm/code/op.go
index 1ce08f7..b4c172a 100644
--- a/pkg/lang/vm/code/op.go
+++ b/pkg/lang/vm/code/op.go
@@ -19,7 +19,9 @@ const (
 
 	OpDrop
 
+	OpAddGlobal
 	OpGetGlobal
+	OpSetGlobal
 	OpGetLocal
 	OpSetLocal
 	OpGetMember
diff --git a/pkg/lang/vm/code/pos.go b/pkg/lang/vm/code/pos.go
new file mode 100644
index 0000000..90deb33
--- /dev/null
+++ b/pkg/lang/vm/code/pos.go
@@ -0,0 +1,13 @@
+package code
+
+type Pos struct {
+	Module int
+	PC     int
+}
+
+func NewPos(module int, pc int) Pos {
+	return Pos{
+		Module: module,
+		PC:     pc,
+	}
+}
\ No newline at end of file
diff --git a/pkg/lang/vm/errors.go b/pkg/lang/vm/errors.go
index bfc8a34..0dd73e7 100644
--- a/pkg/lang/vm/errors.go
+++ b/pkg/lang/vm/errors.go
@@ -9,16 +9,16 @@ import (
 )
 
 type Error struct {
-	Pc   int
+	Pos  code.Pos
 	Line int
 	Err  error
 }
 
 func (e Error) Error() string {
 	if e.Line == -1 {
-		return fmt.Sprintf("vm error at pc %d, unknown line: %v", e.Pc, e.Err)
+		return fmt.Sprintf("vm error in module '%d' at pc %d, unknown line: %v", e.Pos.Module, e.Pos.PC, e.Err)
 	}
-	return fmt.Sprintf("vm error at pc %d, line %d: %v", e.Pc, e.Line, e.Err)
+	return fmt.Sprintf("vm error in module '%d' at pc %d, line %d: %v", e.Pos.Module, e.Pos.PC, e.Line, e.Err)
 }
 
 // Fatal errors
@@ -111,3 +111,27 @@ type ErrWrongNumberOfArguments struct {
 func (e ErrWrongNumberOfArguments) Error() string {
 	return fmt.Sprintf("wrong number of arguments: needed %d, got %d", e.Needed, e.Got)
 }
+
+type ErrCantAddGlobalFromMain struct {
+	GlobalName string
+}
+
+func (e ErrCantAddGlobalFromMain) Error() string {
+	return fmt.Sprintf("can't export '%s' from main module", e.GlobalName)
+}
+
+type ErrGlobalAlreadyExists struct {
+	GlobalName string
+}
+
+func (e ErrGlobalAlreadyExists) Error() string {
+	return fmt.Sprintf("global '%s' already exists", e.GlobalName)
+}
+
+type ErrNoSuchGlobal struct {
+	GlobalName string
+}
+
+func (e ErrNoSuchGlobal) Error() string {
+	return fmt.Sprintf("no such global '%s'", e.GlobalName)
+}
diff --git a/pkg/lang/vm/exec.go b/pkg/lang/vm/exec.go
index c5b0539..5a8eb05 100644
--- a/pkg/lang/vm/exec.go
+++ b/pkg/lang/vm/exec.go
@@ -44,7 +44,7 @@ func (vm *VM) execPushArray() error {
 
 func (vm *VM) execPushFunction(pc int) {
 	// TODO: Make push ops into functions, where the argCount can be passed.
-	vm.stack.Push(value.NewFunction(pc, 0))
+	vm.stack.Push(value.NewFunction(code.NewPos(vm.module(), pc), 0))
 }
 
 func (vm *VM) execPushObject() error {
@@ -57,6 +57,72 @@ func (vm *VM) execPushObject() error {
 	return nil
 }
 
+func (vm *VM) execAddGlobal(name string) error {
+	if !vm.canAddGlobals {
+		return ErrCantAddGlobalFromMain{GlobalName: name}
+	}
+
+	if _, ok := vm.globals[name]; ok {
+		return ErrGlobalAlreadyExists{GlobalName: name}
+	}
+
+	v, err := vm.stack.Pop()
+	if err != nil {
+		return err
+	}
+
+	globalPtr, err := vm.memory.Allocate(mem.CellKindGlobal)
+	if err != nil {
+		return err
+	}
+
+	globalCell := value.GlobalCell(v)
+	if err := vm.memory.Set(globalPtr, globalCell); err != nil {
+		return err
+	}
+
+	vm.globals[name] = globalPtr
+
+	return nil
+}
+
+func (vm *VM) execGetGlobal(name string) error {
+	ptr, ok := vm.globals[name]
+	if !ok {
+		return ErrNoSuchGlobal{GlobalName: name}
+	}
+
+	cell, err := vm.getMemCell(ptr, mem.CellKindGlobal, false)
+	if err != nil {
+		return err
+	}
+
+	v := cell.(value.GlobalCell).Get()
+	v = v.Clone(vm.memory)
+
+	vm.stack.Push(v)
+	return nil
+}
+
+func (vm *VM) execSetGlobal(name string) error {
+	ptr, ok := vm.globals[name]
+	if !ok {
+		return ErrNoSuchGlobal{GlobalName: name}
+	}
+
+	new, err := vm.stack.Pop()
+	if err != nil {
+		return err
+	}
+
+	globalCell := value.GlobalCell(new)
+	if err := vm.memory.Set(ptr, globalCell); err != nil {
+		return err
+	}
+
+	return nil
+}
+
 func (vm *VM) execGetLocal(offset int) error {
 	local, err := vm.stack.Local(int(offset))
 	if err != nil {
@@ -165,7 +231,7 @@ func (vm *VM) execGetMember(name string) error {
 				return err
 			}
 
-			method := value.NewFunction(0, 0).WithData(methodData.WithEnv(envPtr))
+			method := value.NewFunction(code.Pos{}, 0).WithData(methodData.WithEnv(envPtr))
 			// method = method.Clone(vm.memory) will only be necessary when we support methods with environments.
 
 			vm.stack.Push(method)
@@ -219,7 +285,7 @@ func (vm *VM) execGetMember(name string) error {
 
 	member = member.WithEnv(envPtr)
 
-	val := value.NewFunction(0, 0).WithData(member)
+	val := value.NewFunction(code.Pos{}, 0).WithData(member)
 	vm.stack.Push(val)
 
 	parent.Drop(vm.memory)
@@ -781,7 +847,7 @@ func (vm *VM) execCall(argCount uint) error {
 		}
 	}
 
-	if err = vm.stack.PushCall(fn.Pc(), vm.pc, fn.Env()); err != nil {
+	if err = vm.stack.PushCall(fn.Pos(), vm.pos, fn.Env()); err != nil {
 		return err
 	}
 
@@ -806,7 +872,7 @@ func (vm *VM) execCall(argCount uint) error {
 		vm.stack.Push(arg)
 	}
 
-	vm.pc = fn.Pc()
+	vm.setPos(fn.Pos())
 
 	return nil
 }
@@ -821,7 +887,7 @@ func (vm *VM) execJumpIf(pc int, cond bool) error {
 	case value.BoolType:
 		bl := b.Data().(value.BoolData)
 		if bl.Get() == cond {
-			vm.pc = pc
+			vm.setPC(pc)
 		}
 	default:
 		var op code.Op
@@ -846,13 +912,13 @@ func (vm *VM) execRet() error {
 		return err
 	}
 
-	pc, err := vm.popCallAndDrop()
+	pos, err := vm.popCallAndDrop()
 	if err != nil {
 		return err
 	}
 
 	vm.stack.Push(returned)
-	vm.pc = pc
+	vm.setPos(pos)
 	return nil
 }
 
diff --git a/pkg/lang/vm/mem/cell.go b/pkg/lang/vm/mem/cell.go
index 73aa0c6..85d6c34 100644
--- a/pkg/lang/vm/mem/cell.go
+++ b/pkg/lang/vm/mem/cell.go
@@ -12,6 +12,8 @@ const (
 	CellKindEnv
 	CellKindOutlet
 
+	CellKindGlobal
+
 	CellKindForbidden
 )
 
@@ -31,6 +33,8 @@ func (c CellKind) String() string {
 		return "env"
 	case CellKindOutlet:
 		return "outlet"
+	case CellKindGlobal:
+		return "global"
 	case CellKindForbidden:
 		return "forbidden"
 	default:
diff --git a/pkg/lang/vm/stack/errors.go b/pkg/lang/vm/stack/errors.go
index 55ef2ea..55145d5 100644
--- a/pkg/lang/vm/stack/errors.go
+++ b/pkg/lang/vm/stack/errors.go
@@ -11,6 +11,7 @@ var (
 
 	ErrReachedMaxCallDepth  = errors.New("reached max call depth (max depth: 1000)")
 	ErrReachedRootCallFrame = errors.New("reached root call frame")
+	ErrNotAtRootCallFrame   = errors.New("not at root call frame")
 
 	ErrCallBaseCantBeNegative = errors.New("call base cannot be negative")
 )
diff --git a/pkg/lang/vm/stack/stack.go b/pkg/lang/vm/stack/stack.go
index 34ca896..74d4ab8 100644
--- a/pkg/lang/vm/stack/stack.go
+++ b/pkg/lang/vm/stack/stack.go
@@ -1,6 +1,7 @@
 package stack
 
 import (
+	"jinx/pkg/lang/vm/code"
 	"jinx/pkg/lang/vm/mem"
 	"jinx/pkg/lang/vm/value"
 )
@@ -17,8 +18,9 @@ type Stack interface {
 	Len() int
 	IsEmpty() bool
 
-	PushCall(newPc, returnPc int, env mem.Ptr) error
-	PopCall() (int, error)
+	PutRootCall(basePos code.Pos) error
+	PushCall(newPos, returnPos code.Pos, env mem.Ptr) error
+	PopCall() (code.Pos, error)
 
 	CurrentCallEnv() mem.Ptr
 	CallDepth() int
@@ -35,12 +37,6 @@ func New() Stack {
 	data := make([]value.Value, 0, 64)
 	calls := make([]callFrame, 0, 8)
 
-	calls = append(calls, callFrame{
-		pc:       0,
-		returnPc: 0,
-		base:     0,
-	})
-
 	return &stackImpl{
 		data:  data,
 		calls: calls,
@@ -106,30 +102,53 @@ func (stack *stackImpl) IsEmpty() bool {
 	return len(stack.data) == 0
 }
 
-func (stack *stackImpl) PushCall(newPc, returnPc int, env mem.Ptr) error {
+func (stack *stackImpl) PutRootCall(basePos code.Pos) error {
+	frame := callFrame{
+		pos:       basePos,
+		returnPos: basePos,
+		base:      0,
+		env:       mem.NullPtr,
+	}
+
+	if stack.CallDepth() == 0 {
+		stack.calls = append(stack.calls, frame)
+
+		return nil
+	}
+
+	if stack.CallDepth() != 1 {
+		return ErrNotAtRootCallFrame
+	}
+
+	stack.calls[0] = frame
+
+	return nil
+}
+
+func (stack *stackImpl) PushCall(newPos, returnPos code.Pos, env mem.Ptr) error {
 	if stack.CallDepth() == 1000 {
 		return ErrReachedMaxCallDepth
 	}
 
 	stack.calls = append(stack.calls, callFrame{
-		pc:       newPc,
-		returnPc: returnPc,
-		base:     stack.Len(),
-		env:      env,
+		pos:       newPos,
+		returnPos: returnPos,
+		base:      stack.Len(),
+		env:       env,
 	})
 
 	return nil
 }
 
-func (stack *stackImpl) PopCall() (int, error) {
+func (stack *stackImpl) PopCall() (code.Pos, error) {
 	if stack.CallDepth() == 0 {
-		return 0, ErrReachedRootCallFrame
+		return code.Pos{}, ErrReachedRootCallFrame
 	}
 
 	call := stack.topCall()
 	stack.calls = stack.calls[:stack.CallDepth()-1]
 
-	return call.returnPc, nil
+	return call.returnPos, nil
 }
 
 func (stack *stackImpl) CurrentCallEnv() mem.Ptr {
@@ -160,8 +179,8 @@ func (stack *stackImpl) topCall() *callFrame {
 }
 
 type callFrame struct {
-	pc       int     // Beginning of the called function.
-	returnPc int     // Where to return to after the called function returns.
-	base     int     // Base of the local variables on the data stack.
-	env      mem.Ptr // Environment of the called function.
+	pos       code.Pos // Beginning of the called function.
+	returnPos code.Pos // Where to return to after the called function returns.
+	base      int      // Base of the local variables on the data stack.
+	env       mem.Ptr  // Environment of the called function.
 }
diff --git a/pkg/lang/vm/text/decompiler.go b/pkg/lang/vm/text/decompiler.go
index 2b4e704..8a85d49 100644
--- a/pkg/lang/vm/text/decompiler.go
+++ b/pkg/lang/vm/text/decompiler.go
@@ -93,7 +93,9 @@ func (d *Decompiler) decompileInstruction(bc code.Raw) (string, code.Raw) {
 	// Operations that take a string.
 	case code.OpPushString,
 		code.OpPushType,
+		code.OpAddGlobal,
 		code.OpGetGlobal,
+		code.OpSetGlobal,
 		code.OpSetMember,
 		code.OpGetMember:
 		s, rest := d.decompileString(bc[1:])
diff --git a/pkg/lang/vm/text/op.go b/pkg/lang/vm/text/op.go
index ce53f50..ff3c568 100644
--- a/pkg/lang/vm/text/op.go
+++ b/pkg/lang/vm/text/op.go
@@ -17,7 +17,9 @@ var (
 		code.OpPushObject:   "push_object",
 		code.OpPushType:     "push_type",
 		code.OpDrop:         "drop",
+		code.OpAddGlobal:    "add_global",
 		code.OpGetGlobal:    "get_global",
+		code.OpSetGlobal:    "set_global",
 		code.OpGetLocal:     "get_local",
 		code.OpSetLocal:     "set_local",
 		code.OpGetMember:    "get_member",
diff --git a/pkg/lang/vm/utils.go b/pkg/lang/vm/utils.go
index 00311ef..2b7fa6f 100644
--- a/pkg/lang/vm/utils.go
+++ b/pkg/lang/vm/utils.go
@@ -1,6 +1,7 @@
 package vm
 
 import (
+	"jinx/pkg/lang/vm/code"
 	"jinx/pkg/lang/vm/mem"
 	"jinx/pkg/lang/vm/value"
 )
@@ -14,14 +15,14 @@ func (vm *VM) popAndDrop() (value.Value, error) {
 	return v, nil
 }
 
-func (vm *VM) popCallAndDrop() (int, error) {
+func (vm *VM) popCallAndDrop() (code.Pos, error) {
 	envPtr := vm.stack.CurrentCallEnv()
 	vm.memory.Release(envPtr)
 
 	for !vm.stack.ReachedBaseOfCall() {
 		_, err := vm.popAndDrop()
 		if err != nil {
-			return 0, err
+			return code.Pos{}, err
 		}
 	}
 
@@ -63,6 +64,8 @@ func (vm *VM) getMemCell(ptr mem.Ptr, kind mem.CellKind, allowNil bool) (mem.Cel
 		_, ok = cell.(value.TypeCell)
 	case mem.CellKindObject:
 		_, ok = cell.(value.ObjectCell)
+	case mem.CellKindGlobal:
+		_, ok = cell.(value.GlobalCell)
 	}
 
 	if !ok {
@@ -71,3 +74,23 @@ func (vm *VM) getMemCell(ptr mem.Ptr, kind mem.CellKind, allowNil bool) (mem.Cel
 
 	return cell, nil
 }
+
+func (vm *VM) module() int {
+	return vm.pos.Module
+}
+
+func (vm *VM) pc() int {
+	return vm.pos.PC
+}
+
+func (vm *VM) setPC(pc int) {
+	vm.pos.PC = pc
+}
+
+func (vm *VM) advancePC(by int) {
+	vm.pos.PC += by
+}
+
+func (vm *VM) setPos(pos code.Pos) {
+	vm.pos = pos
+}
diff --git a/pkg/lang/vm/value/cells.go b/pkg/lang/vm/value/cells.go
index 5abb032..19ecfde 100644
--- a/pkg/lang/vm/value/cells.go
+++ b/pkg/lang/vm/value/cells.go
@@ -1,6 +1,9 @@
 package value
 
-import "jinx/pkg/lang/vm/mem"
+import (
+	"jinx/pkg/lang/vm/code"
+	"jinx/pkg/lang/vm/mem"
+)
 
 type ArrayCell []Value
 
@@ -55,7 +58,7 @@ func (t TypeCell) DropCell(m mem.Mem) {
 	typ := t.Get()
 	for _, f := range typ.Methods {
 		// Wrap data in a Value to drop it.
-		val := NewFunction(0, 0).WithData(f)
+		val := NewFunction(code.Pos{}, 0).WithData(f)
 		val.Drop(m)
 	}
 
@@ -101,3 +104,17 @@ func (e EnvCell) MatchingCellKind() mem.CellKind {
 func (e EnvCell) Get() Env {
 	return Env(e)
 }
+
+type GlobalCell Value
+
+func (g GlobalCell) DropCell(m mem.Mem) {
+	panic("global cell cannot be dropped")
+}
+
+func (g GlobalCell) MatchingCellKind() mem.CellKind {
+	return mem.CellKindGlobal
+}
+
+func (g GlobalCell) Get() Value {
+	return Value(g)
+}
diff --git a/pkg/lang/vm/value/data.go b/pkg/lang/vm/value/data.go
index 18e1b3d..6c3d762 100644
--- a/pkg/lang/vm/value/data.go
+++ b/pkg/lang/vm/value/data.go
@@ -2,6 +2,7 @@ package value
 
 import (
 	"fmt"
+	"jinx/pkg/lang/vm/code"
 	"jinx/pkg/lang/vm/mem"
 	"strconv"
 	"strings"
@@ -127,7 +128,7 @@ func (n NullData) String(_ mem.Mem) (string, error) {
 }
 
 type FunctionData struct {
-	pc     int
+	pos    code.Pos
 	args   uint
 	env    mem.Ptr
 	native NativeFunc
@@ -135,8 +136,8 @@ type FunctionData struct {
 
 type NativeFunc func([]Value) (Value, error)
 
-func (f FunctionData) Pc() int {
-	return f.pc
+func (f FunctionData) Pos() code.Pos {
+	return f.pos
 }
 
 func (f FunctionData) Args() uint {
@@ -152,18 +153,18 @@ func (f FunctionData) Native() NativeFunc {
 }
 
 func (f FunctionData) WithEnv(env mem.Ptr) FunctionData {
-	return FunctionData{pc: f.pc, args: f.args, env: env, native: f.native}
+	return FunctionData{pos: f.pos, args: f.args, env: env, native: f.native}
 }
 
 func (f FunctionData) WithArgs(args uint) FunctionData {
-	return FunctionData{pc: f.pc, args: args, env: f.env, native: f.native}
+	return FunctionData{pos: f.pos, args: args, env: f.env, native: f.native}
 }
 
 func (f FunctionData) String(_ mem.Mem) (string, error) {
 	if f.native != nil {
 		return fmt.Sprintf("<fn(%d) native>", f.args), nil
 	} else {
-		return fmt.Sprintf("<fn(%d) %d>", f.args, f.pc), nil
+		return fmt.Sprintf("<fn(%d) %d:%d>", f.args, f.pos.Module, f.pos.PC), nil
 	}
 }
 
diff --git a/pkg/lang/vm/value/value.go b/pkg/lang/vm/value/value.go
index 5dd5012..b051f04 100644
--- a/pkg/lang/vm/value/value.go
+++ b/pkg/lang/vm/value/value.go
@@ -1,6 +1,7 @@
 package value
 
 import (
+	"jinx/pkg/lang/vm/code"
 	"jinx/pkg/lang/vm/mem"
 )
 
@@ -52,8 +53,8 @@ func NewNull() Value {
 	return Value{t: CORE_TYPE_NULL, d: NullData{}}
 }
 
-func NewFunction(pc int, args uint) Value {
-	return Value{t: CORE_TYPE_FUNCTION, d: FunctionData{pc: pc, args: args}}
+func NewFunction(pos code.Pos, args uint) Value {
+	return Value{t: CORE_TYPE_FUNCTION, d: FunctionData{pos: pos, args: args}}
 }
 
 func NewNativeFunction(f NativeFunc, args uint) Value {
diff --git a/pkg/lang/vm/vm.go b/pkg/lang/vm/vm.go
index 8b47915..4a4aa68 100644
--- a/pkg/lang/vm/vm.go
+++ b/pkg/lang/vm/vm.go
@@ -7,18 +7,28 @@ import (
 )
 
 type VM struct {
-	code   *code.Code
-	pc     int
+	pos code.Pos
+
+	modules []*code.Code
+
 	stack  stack.Stack
 	memory mem.Mem
+
+	canAddGlobals bool
+	globals       map[string]mem.Ptr
 }
 
-func New(code *code.Code) *VM {
+func New(main *code.Code, deps []*code.Code) *VM {
 	vm := &VM{
-		code:   code,
-		pc:     0,
+		pos: code.NewPos(0, 0),
+
+		modules: append([]*code.Code{main}, deps...),
+
 		stack:  stack.New(),
 		memory: mem.New(),
+
+		canAddGlobals: false,
+		globals:       make(map[string]mem.Ptr),
 	}
 
 	if err := vm.setup(); err != nil {
@@ -46,14 +56,56 @@ func (vm *VM) GetResult() (string, error) {
 }
 
 func (vm *VM) Run() error {
-	for vm.pc < vm.code.Len() {
-		op, advance := vm.code.GetOp(vm.pc)
-		vm.pc += advance
+	vm.canAddGlobals = true
+	for i := 1; i < len(vm.modules); i++ {
+		if err := vm.executeModule(i); err != nil {
+			return err
+		}
+
+		// Drop all calls from the stack after the module has finished
+		for vm.stack.CallDepth() > 1 {
+			if _, err := vm.popCallAndDrop(); err != nil {
+				return err
+			}
+		}
+
+		// Drop the root stack values
+		for !vm.stack.IsEmpty() {
+			if _, err := vm.popAndDrop(); err != nil {
+				return err
+			}
+		}
+	}
+
+	vm.canAddGlobals = false
+	if err := vm.executeModule(0); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (vm *VM) executeModule(moduleID int) error {
+	vm.pos = code.NewPos(moduleID, 0)
+
+	if err := vm.stack.PutRootCall(vm.pos); err != nil {
+		return err
+	}
+
+	for {
+		module := vm.modules[vm.module()]
 
-		if decision, err := vm.step(op); err != nil {
+		if vm.pc() >= module.Len() {
+			return nil
+		}
+
+		op, advance := module.GetOp(vm.pc())
+		vm.advancePC(advance)
+
+		if decision, err := vm.step(module, op); err != nil {
 			return Error{
-				Pc:   vm.pc,
-				Line: vm.code.Debug().PCToLine(vm.pc),
+				Pos:  vm.pos,
+				Line: module.Debug().PCToLine(vm.pc()),
 				Err:  err,
 			}
 		} else if decision == stepDecisionHalt {
@@ -71,7 +123,7 @@ const (
 	stepDecisionHalt
 )
 
-func (vm *VM) step(op code.Op) (stepDecision, error) {
+func (vm *VM) step(module *code.Code, op code.Op) (stepDecision, error) {
 	var err error
 	switch op {
 	case code.OpNop:
@@ -80,18 +132,18 @@ func (vm *VM) step(op code.Op) (stepDecision, error) {
 		return stepDecisionHalt, nil
 
 	case code.OpPushInt:
-		x, advance := vm.code.GetInt(vm.pc)
-		vm.pc += advance
+		x, advance := module.GetInt(vm.pc())
+		vm.advancePC(advance)
 
 		vm.execPushInt(x)
 	case code.OpPushFloat:
-		x, advance := vm.code.GetFloat(vm.pc)
-		vm.pc += advance
+		x, advance := module.GetFloat(vm.pc())
+		vm.advancePC(advance)
 
 		vm.execPushFloat(x)
 	case code.OpPushString:
-		str, advance := vm.code.GetString(vm.pc)
-		vm.pc += advance
+		str, advance := module.GetString(vm.pc())
+		vm.advancePC(advance)
 
 		err = vm.execPushString(str)
 	case code.OpPushNull:
@@ -103,60 +155,73 @@ func (vm *VM) step(op code.Op) (stepDecision, error) {
 	case code.OpPushArray:
 		vm.execPushArray()
 	case code.OpPushFunction:
-		x, advance := vm.code.GetUint(vm.pc)
-		vm.pc += advance
+		x, advance := module.GetUint(vm.pc())
+		vm.advancePC(advance)
 
 		vm.execPushFunction(int(x))
 	case code.OpPushObject:
 		err = vm.execPushObject()
 	case code.OpPushType:
-		name, advance := vm.code.GetString(vm.pc)
-		vm.pc += advance
+		name, advance := module.GetString(vm.pc())
+		vm.advancePC(advance)
 
 		err = vm.execPushType(name)
 
 	case code.OpDrop:
-		dropAmount, advance := vm.code.GetUint(vm.pc)
-		vm.pc += advance
+		dropAmount, advance := module.GetUint(vm.pc())
+		vm.advancePC(advance)
 
 		err = vm.execDrop(uint(dropAmount))
 
+	case code.OpAddGlobal:
+		globalName, advance := module.GetString(vm.pc())
+		vm.advancePC(advance)
+
+		err = vm.execAddGlobal(globalName)
 	case code.OpGetGlobal:
-		panic("not implemented")
+		globalName, advance := module.GetString(vm.pc())
+		vm.advancePC(advance)
+
+		err = vm.execGetGlobal(globalName)
+	case code.OpSetGlobal:
+		globalName, advance := module.GetString(vm.pc())
+		vm.advancePC(advance)
+
+		err = vm.execSetGlobal(globalName)
 	case code.OpGetLocal:
-		offset, advance := vm.code.GetInt(vm.pc)
-		vm.pc += advance
+		offset, advance := module.GetInt(vm.pc())
+		vm.advancePC(advance)
 
 		err = vm.execGetLocal(int(offset))
 	case code.OpSetLocal:
-		offset, advance := vm.code.GetInt(vm.pc)
-		vm.pc += advance
+		offset, advance := module.GetInt(vm.pc())
+		vm.advancePC(advance)
 
 		err = vm.execSetLocal(int(offset))
 	case code.OpGetMember:
-		name, advance := vm.code.GetString(vm.pc)
-		vm.pc += advance
+		name, advance := module.GetString(vm.pc())
+		vm.advancePC(advance)
 
 		err = vm.execGetMember(name)
 	case code.OpSetMember:
-		name, advance := vm.code.GetString(vm.pc)
-		vm.pc += advance
+		name, advance := module.GetString(vm.pc())
+		vm.advancePC(advance)
 
 		err = vm.execSetMember(name)
 
 	case code.OpGetEnv:
-		envIndex, advance := vm.code.GetUint(vm.pc)
-		vm.pc += advance
+		envIndex, advance := module.GetUint(vm.pc())
+		vm.advancePC(advance)
 
 		err = vm.execGetEnv(int(envIndex))
 	case code.OpSetEnv:
-		envIndex, advance := vm.code.GetUint(vm.pc)
-		vm.pc += advance
+		envIndex, advance := module.GetUint(vm.pc())
+		vm.advancePC(advance)
 
 		err = vm.execSetEnv(int(envIndex))
 	case code.OpAddToEnv:
-		local, advance := vm.code.GetUint(vm.pc)
-		vm.pc += advance
+		local, advance := module.GetUint(vm.pc())
+		vm.advancePC(advance)
 
 		err = vm.execAddToEnv(int(local))
 
@@ -164,8 +229,8 @@ func (vm *VM) step(op code.Op) (stepDecision, error) {
 		err = vm.execAnchorType()
 
 	case code.OpSetArgCount:
-		argCount, advance := vm.code.GetUint(vm.pc)
-		vm.pc += advance
+		argCount, advance := module.GetUint(vm.pc())
+		vm.advancePC(advance)
 
 		err = vm.execSetArgCount(uint(argCount))
 
@@ -193,21 +258,21 @@ func (vm *VM) step(op code.Op) (stepDecision, error) {
 	case code.OpIndex:
 		err = vm.execIndex()
 	case code.OpCall:
-		argCount, advance := vm.code.GetUint(vm.pc)
-		vm.pc += advance
+		argCount, advance := module.GetUint(vm.pc())
+		vm.advancePC(advance)
 
 		err = vm.execCall(uint(argCount))
 
 	case code.OpJmp:
-		pc, _ := vm.code.GetUint(vm.pc)
-		vm.pc = int(pc)
+		pc, _ := module.GetUint(vm.pc())
+		vm.setPC(int(pc))
 	case code.OpJt:
-		pc, advance := vm.code.GetUint(vm.pc)
-		vm.pc += advance
+		pc, advance := module.GetUint(vm.pc())
+		vm.advancePC(advance)
 		err = vm.execJumpIf(int(pc), true)
 	case code.OpJf:
-		pc, advance := vm.code.GetUint(vm.pc)
-		vm.pc += advance
+		pc, advance := module.GetUint(vm.pc())
+		vm.advancePC(advance)
 		err = vm.execJumpIf(int(pc), false)
 	case code.OpRet:
 		err = vm.execRet()
diff --git a/pkg/lang/vm/vm_test.go b/pkg/lang/vm/vm_test.go
index ae0b8e6..b25a446 100644
--- a/pkg/lang/vm/vm_test.go
+++ b/pkg/lang/vm/vm_test.go
@@ -440,9 +440,50 @@ func TestPrimes(t *testing.T) {
 	test(t, src, "[2, 3, 5, 7]")
 }
 
+func TestModules(t *testing.T) {
+	mainSrc := `
+	get_global "add_one"
+	get_global "x"
+	call 1
+	halt
+	`
+
+	librarySrc1 := `
+	push_int 41
+	add_global "x"
+	halt
+	`
+
+	librarySrc2 := `
+	push_function @add_one
+	set_arg_count 1
+	add_global "add_one"
+	halt
+
+	@add_one:
+	get_local 0
+	push_int 1
+	add
+	ret
+	`
+
+	main := compile(t, mainSrc)
+	library1 := compile(t, librarySrc1)
+	library2 := compile(t, librarySrc2)
+
+	vm := vm.New(&main, []*code.Code{&library1, &library2})
+	err := vm.Run()
+	require.NoError(t, err)
+
+	res, err := vm.GetResult()
+	require.NoError(t, err)
+
+	require.Equal(t, "42", res)
+}
+
 func test(t *testing.T, src string, expected string) {
 	bc := compile(t, src)
-	vm := vm.New(&bc)
+	vm := vm.New(&bc, nil)
 	err := vm.Run()
 	require.NoError(t, err)