Remove BACK symbol

README.md

@@ -10,7 +10,6 @@ Original motivation was to create a simple templating renderer for USSD clients,
 
 The VM defines the following opcode symbols:
 
-* `BACK` - Return to the previous execution frame (will fail if at top frame). It leaves to the state of the execution layer to define what "previous" means.
 * `CATCH <symbol> <signal>` - Jump to symbol if signal is set (see `signals` below).
 * `CROAK <signal>` - Clear state and restart execution from top if signal is set (see `signals` below).
 * `LOAD <symbol> <size>` - Execute the code symbol `symbol` and cache the data, constrained to the given `size`. Can be exposed with `MAP` within scope, 

go/vm/opcodes.go

@@ -6,7 +6,7 @@ type Opcode uint16
 
 // VM Opcodes
 const (
-	BACK = 0
+	NOOP = 0
 	CATCH = 1
 	CROAK = 2
 	LOAD = 3

go/vm/runner.go

@@ -38,8 +38,6 @@ func Run(instruction []byte, st *state.State, rs resource.Resource, ctx context.
 			instruction, err = RunMap(instruction[2:], st, rs, ctx)
 		case MOVE:
 			instruction, err = RunMove(instruction[2:], st, rs, ctx)
-		case BACK:
-			instruction, err = RunBack(instruction[2:], st, rs, ctx)
 		case INCMP:
 			instruction, err = RunIncmp(instruction[2:], st, rs, ctx)
 		case HALT: