Introduce calls

elm.go

@@ -26,6 +26,8 @@ const (
 	EQ Operation = 8
 	JMP Operation = 9
 	JMPIF Operation = 10
+	CALL Operation = 11
+	RET Operation = 12
 )
 
 type Inst struct {
@@ -33,9 +35,31 @@ type Inst struct {
 	Operand int32
 }
 
+type Frame struct {
+	Locals map[int]int32
+	ReturnAddress int
+}
+
+func CreateFrame(returnAddress int32) *Frame {
+	f := Frame{}
+	f.Locals = make(map[int]int32)
+	f.ReturnAddress = int(returnAddress)
+
+	return &f
+}
+
+func (f *Frame) StoreVariable(address int, value int32) {
+	f.Locals[address] = value
+}
+
+func (f *Frame) GetVariable(address int) int32 {
+	return f.Locals[address]
+}
+ 
 type Machine struct {
 	program []Inst
 	stack []int32
+	stackFrame []*Frame
 	ip int32
 	sp int32
 	isHalted bool;
@@ -45,6 +69,8 @@ func Constructor() *Machine {
 	m := Machine{}
 	m.program = make([]Inst, 0)
 	m.stack = make([]int32, STACK_SIZE)
+	m.stackFrame = make([]*Frame, 0)
+	m.stackFrame = append(m.stackFrame, CreateFrame(0))
 	m.ip = 0
 	m.sp = 0
 	m.isHalted = false
@@ -165,6 +191,21 @@ func (m* Machine) Execute() error {
 		} else {
 			m.ip++
 		}
+	case CALL:
+		if (int32(len(m.program) - 1) < instr.Operand || instr.Operand < 0) {
+			return errors.New("Illegal access")
+		}
+
+		m.stackFrame = append(m.stackFrame, CreateFrame(m.ip + 1))
+		m.ip = instr.Operand
+	case RET:
+		if len(m.stackFrame) < 2 {
+			return errors.New("Stackframe underflow")
+		}
+
+		currentFrame := m.stackFrame[len(m.stackFrame) - 1]
+		m.stackFrame = m.stackFrame[:len(m.stackFrame) - 1]
+		m.ip = int32(currentFrame.ReturnAddress)
 	}
 	return nil
 }
@@ -269,6 +310,14 @@ func (m* Machine) InterpretProgramFromFile(filename string) error {
 			m.Push(Inst{Operation: JMP, Operand: int32(op)})
 		} else if (strings.HasPrefix(line, "EQ")) {
 			m.Push(Inst{Operation: EQ})
+		} else if (strings.HasPrefix(line, "CALL")) {
+			op, err := strconv.Atoi(strings.Fields(line)[1])
+			if err != nil {
+				return err
+			}
+			m.Push(Inst{Operation: CALL, Operand: int32(op)})
+		} else if (strings.HasPrefix(line, "RET")) {
+			m.Push(Inst{Operation: RET})
 		}
     }