first commit

1 files changed, 27 insertions, 0 deletions

diff --git a/stack.go b/stack.go
new file mode 100644
index 0000000..c0850d4
--- /dev/null
+++ b/stack.go
@@ -0,0 +1,27 @@
+package expression
+
+type Stack []Token
+
+func (s *Stack) Push(item Token) {
+	*s = append(*s, item)
+}
+
+func (s *Stack) Pop() (item Token) {
+	if len(*s) == 0 {
+		return
+	}
+
+	*s, item = (*s)[:len(*s)-1], (*s)[len(*s)-1]
+	return item
+}
+
+func (s *Stack) Empty() bool {
+	return len(*s) == 0
+}
+
+func (s *Stack) Head() (item *Token) {
+	if s.Empty() {
+		return nil
+	}
+	return &((*s)[len(*s)-1])
+}