Make Next() method on Context failable

refactor peekContext and Peek

pkg/vm/stack/context.go

@@ -41,12 +41,12 @@ func (c *Context) Context() (*Context, error) {
 }
 
 // Next return the next instruction to execute.
-func (c *Context) Next() Instruction {
+func (c *Context) Next() (Instruction, error) {
 	c.ip++
 	if c.ip >= len(c.prog) {
-		return RET
+		return RET, errors.New("program pointer is more than the length of program. RETURNING")
 	}
-	return Instruction(c.prog[c.ip])
+	return Instruction(c.prog[c.ip]), nil
 }
 
 // IP returns the absolute instruction without taking 0 into account.

pkg/vm/stack/invocation.go

@@ -21,11 +21,7 @@ func (i *Invocation) peekContext(n uint16) (*Context, error) {
 	if err != nil {
 		return nil, err
 	}
-	ctx, err := item.Context()
-	if err != nil {
-		return nil, err
-	}
-	return ctx, nil
+	return item.Context()
 }
 
 // CurrentContext returns the current context on the invocation stack
@@ -33,6 +29,13 @@ func (i *Invocation) CurrentContext() (*Context, error) {
 	return i.peekContext(0)
 }
 
+// RemoveCurrentContext removes the context on the top of the invocation stack
+// This is a convenience method for Pop
+func (i *Invocation) RemoveCurrentContext() error {
+	_, err := i.Pop()
+	return err
+}
+
 // CallingContext will return the cntext item
 // that will be called next.
 func (i *Invocation) CallingContext() (*Context, error) {

pkg/vm/stack/stack.go

@@ -106,15 +106,14 @@ func (ras *RandomAccess) Peek(n uint16) (Item, error) {
 		return ras.vals[index], nil
 	}
 
-	if ras.vals == nil {
-		return nil, errors.New("Cannot peak at a nil stack")
+	if ras.Len() < 1 {
+		return nil, fmt.Errorf("cannot peak at a stack with no item, length of stack is %d", ras.Len())
 	}
 
 	// Check that we are not peeking out of the bounds
 	if n > stackSize-1 {
 		return nil, fmt.Errorf("Tried to peek at index %d when length of stack is %d", n, len(ras.vals))
 	}
-
 	index := stackSize - n - 1
 
 	return ras.vals[index], nil
@@ -131,3 +130,13 @@ func (ras *RandomAccess) PopInt() (*Int, error) {
 	}
 	return item.Integer()
 }
+
+// PopByteArray will remove the last stack item that was added
+// And cast it to an ByteArray
+func (ras *RandomAccess) PopByteArray() (*ByteArray, error) {
+	item, err := ras.Pop()
+	if err != nil {
+		return nil, err
+	}
+	return item.ByteArray()
+}