Add catch implementation

go/state/state.go

@@ -126,6 +126,11 @@ func(st *State) FlagBitSize() uint32 {
 	return st.bitSize
 }
 
+// FlagBitSize reports the amount of bits available in the bit field index.
+func(st *State) FlagByteSize() uint8 {
+	return uint8(len(st.Flags))
+}
+
 // GetIndex scans a byte slice in same order as in storage, and returns the index of the first set bit.
 //
 // If the given byte slice is too small for the bit field bitsize, the check will terminate at end-of-data without error.

go/vm/vm.go

@@ -120,13 +120,22 @@ func RunCatch(instruction []byte, st state.State, rs resource.Resource, ctx cont
 	if err != nil {
 		return st, instruction, err
 	}
-	r, err := rs.Get(head)
-	if err != nil {
-		return st, instruction, err
+	// TODO: perhaps check against the registered byte size
+	//l := st.FlagByteSize()
+	bitFieldSize := tail[0]
+	bitField := tail[1:1+bitFieldSize]
+	tail = tail[1+bitFieldSize:]
+	if st.GetIndex(bitField) {
+		log.Printf("catch at flag %v, moving to %v", bitField, head)
+//		r, err := rs.Get(head)
+//		if err != nil {
+//			return st, instruction, err
+//		}
+		//st.Add(head, r, 0)
+		st.Down(head)
+		tail = []byte{}
 	} 
-	_ = tail
-	st.Add(head, r, 0)
-	return st, []byte{}, nil
+	return st, tail, nil
 }
 
 // RunMap executes the CROAK opcode

go/vm/vm_test.go

@@ -51,6 +51,7 @@ func (r *TestResource) Get(sym string) (string, error) {
 	case "three":
 		return "{{.one}} inky pinky {{.three}} blinky clyde {{.two}}", nil
 	}
+	panic(fmt.Sprintf("unknown symbol %s", sym))
 	return "", fmt.Errorf("unknown symbol %s", sym)
 }
 
@@ -89,7 +90,7 @@ func (r *TestResource) FuncFor(sym string) (resource.EntryFunc, error) {
 func TestRun(t *testing.T) {
 	st := state.NewState(5)
 	rs := TestResource{}
-	b := []byte{0x00, 0x01, 0x03}
+	b := []byte{0x00, MOVE, 0x03}
 	b = append(b, []byte("foo")...)
 	r, _, err := Run(b, st, &rs, context.TODO())
 	if err != nil {
@@ -339,3 +340,34 @@ func TestRunMoveAndBack(t *testing.T) {
 		t.Errorf("expected where-string 'bar', got %v", loc)
 	}
 }
+
+func TestCatchAndBack(t *testing.T) {
+	st := state.NewState(5)
+	rs := TestResource{}
+	rt := router.NewRouter()
+	rt.Add("foo", "bar")
+	b := NewLine([]byte{}, LOAD, []string{"one"}, nil, []uint8{0})
+	b = NewLine(b, CATCH, []string{"bar"}, []byte{0x04}, nil)
+	b = NewLine(b, MOVE, []string{"foo"}, nil, nil)
+	st, _, err := Run(b, st, &rs, context.TODO())
+	if err != nil {
+		t.Error(err)
+	}
+	r := st.Where()
+	if r != "foo" {
+		t.Errorf("expected where-symbol 'foo', got %v", r)
+	}
+
+	st.SetFlag(2)
+	b = NewLine([]byte{}, LOAD, []string{"two"}, nil, []uint8{0})
+	b = NewLine(b, CATCH, []string{"bar"}, []byte{0x04}, nil)
+	b = NewLine(b, MOVE, []string{"foo"}, nil, nil)
+	st, _, err = Run(b, st, &rs, context.TODO())
+	if err != nil {
+		t.Error(err)
+	}
+	r = st.Where()
+	if r != "bar" {
+		t.Errorf("expected where-symbol 'bar', got %v", r)
+	}
+}