1 files changed, 9 insertions, 3 deletions
diff --git a/stack.go b/stack.go
index 182d418..1a52e94 100644
--- a/stack.go
+++ b/stack.go
@@ -6,11 +6,17 @@ func (s *Stack) push(v float64) {
 	*s = append(*s, v)
 }
 
-func (s *Stack) pop() *float64 {
+func (s *Stack) pop() (float64, error) {
 	if len(*s) > 0 {
 		v := (*s)[len(*s)-1]
 		*s = (*s)[:len(*s)-1]
-		return &v
+		return v, nil
 	}
-	return nil
+	return 0, EmptyStackErr{}
+}
+
+type EmptyStackErr struct{}
+
+func (e EmptyStackErr) Error() string {
+	return "empty stack"
 }