Split lexer from parent project

1 files changed, 38 insertions, 0 deletions

diff --git a/stack.go b/stack.go
new file mode 100644
index 0000000..2ecc44d
--- /dev/null
+++ b/stack.go
@@ -0,0 +1,38 @@
+package lexer
+
+type stackNode struct {
+	r    rune
+	next *stackNode
+}
+
+type stack struct {
+	start *stackNode
+}
+
+func newStack() stack {
+	return stack{}
+}
+
+func (s *stack) push(r rune) {
+	node := &stackNode{r: r}
+	if s.start == nil {
+		s.start = node
+	} else {
+		node.next = s.start
+		s.start = node
+	}
+}
+
+func (s *stack) pop() rune {
+	if s.start == nil {
+		return EOFRune
+	}
+
+	n := s.start
+	s.start = n.next
+	return n.r
+}
+
+func (s *stack) clear() {
+	s.start = nil
+}