From 7ab0aba088c0c654e64773d62be48ba660d6cb85 Mon Sep 17 00:00:00 2001
From: Ian Gulliver <git@flamingcow.io>
Date: Tue, 16 Nov 2021 15:27:30 -1000
Subject: [PATCH] More private members

---
 instruction.go | 30 ++++++++++++++++++++++++++----
 ophandler.go   |  4 ++--
 state.go       | 18 ++++--------------
 3 files changed, 32 insertions(+), 20 deletions(-)

diff --git a/instruction.go b/instruction.go
index 40dace8..fffddba 100644
--- a/instruction.go
+++ b/instruction.go
@@ -5,18 +5,18 @@ import "bytes"
 import "github.com/lunixbochs/struc"
 import "github.com/pkg/errors"
 
-const InstructionBytes = 32
-
 type Instruction struct {
 	OpCode   OpCodeType
 	Reserved [4]byte
 	Operand1 Operand
 	Operand2 Operand
 
-	opHandler OpHandler `struc:"skip"`
+	opHandler opHandler `struc:"skip"`
 }
 
-func NewInstruction(byteCode []byte) (*Instruction, error) {
+const instructionBytes = 32
+
+func NewInstructionFromByteCode(byteCode []byte) (*Instruction, error) {
 	instr := &Instruction{}
 
 	reader := bytes.NewReader(byteCode)
@@ -28,3 +28,25 @@ func NewInstruction(byteCode []byte) (*Instruction, error) {
 
 	return instr, nil
 }
+
+func NewInstructionsFromByteCode(byteCode []byte) ([]*Instruction, error) {
+	instrs := []*Instruction{}
+
+	for start := 0; start < len(byteCode); start += instructionBytes {
+		chunk := byteCode[start : start+instructionBytes]
+		instr, err := NewInstructionFromByteCode(chunk)
+		if err != nil {
+			return nil, errors.Wrapf(err, "At byte offset %d", start)
+		}
+		instrs = append(instrs, instr)
+	}
+
+	if len(instrs) == 0 || instrs[len(instrs)-1].OpCode != OpReturn {
+		// Add implicit return at the end of each function
+		instrs = append(instrs, &Instruction{
+			OpCode: OpReturn,
+		})
+	}
+
+	return instrs, nil
+}
diff --git a/ophandler.go b/ophandler.go
index 0dc266a..e35d8b7 100644
--- a/ophandler.go
+++ b/ophandler.go
@@ -1,8 +1,8 @@
 package vm
 
-type OpHandler func(*State, *Instruction)
+type opHandler func(*State, *Instruction)
 
-var OpHandlers = map[OpCodeType]OpHandler{
+var opHandlers = map[OpCodeType]opHandler{
 	OpNoOp:   (*State).NoOp,
 	OpCall:   (*State).Call,
 	OpReturn: (*State).Return,
diff --git a/state.go b/state.go
index 2fd02c7..5fc263d 100644
--- a/state.go
+++ b/state.go
@@ -23,21 +23,11 @@ func NewState(byteCodes [][]byte) (*State, error) {
 	state := &State{}
 
 	for i, byteCode := range byteCodes {
-		instrs := []*Instruction{}
-
-		for start := 0; start < len(byteCode); start += InstructionBytes {
-			chunk := byteCode[start : start+InstructionBytes]
-			instr, err := NewInstruction(chunk)
-			if err != nil {
-				return nil, errors.Wrapf(err, "At function index %d, byte offset %d", i, start)
-			}
-			instrs = append(instrs, instr)
+		instrs, err := NewInstructionsFromByteCode(byteCode)
+		if err != nil {
+			return nil, errors.Wrapf(err, "At function index %d", i)
 		}
 
-		instrs = append(instrs, &Instruction{
-			OpCode: OpReturn,
-		})
-
 		state.functions = append(state.functions, instrs)
 	}
 
@@ -70,7 +60,7 @@ func (state *State) setError(err error) {
 func (state *State) setHandlers() {
 	for _, fnc := range state.functions {
 		for _, instr := range fnc {
-			handler, found := OpHandlers[instr.OpCode]
+			handler, found := opHandlers[instr.OpCode]
 			if !found {
 				state.setError(fmt.Errorf("Invalid OpCode: 0x%08x", instr.OpCode))
 				return