diff --git a/go/state/state.go b/go/state/state.go
index 15fd388..c1665b9 100644
--- a/go/state/state.go
+++ b/go/state/state.go
@@ -1,6 +1,7 @@
 package state
 
 import (
+	"fmt"
 )
 
 type State struct {
@@ -40,10 +41,30 @@ func(st *State) Enter(input string) {
 }
 
 func(st *State) Add(k string, v string) error {
+	sz := st.checkCapacity(v)
+	if sz == 0 {
+		return fmt.Errorf("Cache capacity exceeded %v of %v", st.CacheUseSize + sz, st.CacheSize)
+	}
+	fmt.Printf("len %v %v\n", sz, st.CacheUseSize)
 	st.Cache[len(st.Cache)-1][k] = v
+	st.CacheUseSize += sz
 	return nil
 }
 
 func(st *State) Get() (map[string]string, error) {
 	return st.Cache[len(st.Cache)-1], nil
 }
+
+func (st *State) Exit() {
+}
+
+func(st *State) checkCapacity(v string) uint32 {
+	sz := uint32(len(v))
+	if st.CacheSize == 0 {
+		return sz
+	}
+	if st.CacheUseSize + sz > st.CacheSize {
+		return 0	
+	}
+	return sz
+}
diff --git a/go/state/state_test.go b/go/state/state_test.go
index 7c15f4c..f44ecb4 100644
--- a/go/state/state_test.go
+++ b/go/state/state_test.go
@@ -34,6 +34,18 @@ func TestNewStateCache(t *testing.T) {
 
 func TestStateCacheUse(t *testing.T) {
 	st := NewState(17, 0)
+	st = st.WithCacheSize(10)
 	st.Enter("foo")
-	st.Add("bar", "baz")
+	err := st.Add("bar", "baz")
+	if err != nil {
+		t.Error(err)
+	}
+	err = st.Add("inky", "pinky")
+	if err != nil {
+		t.Error(err)
+	}
+	err = st.Add("blinky", "clyde")
+	if err == nil {
+		t.Errorf("expected capacity error")
+	}
 }
diff --git a/go/vm/vm_test.go b/go/vm/vm_test.go
index 16627c7..dbdfa8f 100644
--- a/go/vm/vm_test.go
+++ b/go/vm/vm_test.go
@@ -124,6 +124,4 @@ func TestRunMap(t *testing.T) {
 	if r != expect {
 		t.Errorf("Expected %v, got %v", expect, r)
 	}
-
-
 }