add stdlib package with readme

ast/tokenstack.go

@@ -0,0 +1,39 @@
+/*   SHS: Syntactically Homogeneous Shell
+ *   Copyright (C) 2019  Aidan Hahn
+ *
+ *   This program is free software: you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation, either version 3 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package ast
+
+type TokenStack struct {
+    buffer []*Token
+    capacity int
+}
+
+func (s *TokenStack) Push(v *Token) {
+    s.capacity++
+    s.buffer = append(s.buffer, v)
+}
+
+func (s *TokenStack) Pop() *Token {
+    if s.capacity <= 0 {
+        return nil
+    }
+
+    s.capacity--
+    res := s.buffer[len(s.buffer) - 1]
+    s.buffer = s.buffer[:len(s.buffer) - 1]
+    return res
+}