From 111657b567889763f55bfa4db5636b2ce9d2e95e Mon Sep 17 00:00:00 2001
From: greg <greg.shuflin@protonmail.com>
Date: Thu, 10 May 2018 22:23:42 -0700
Subject: [PATCH] Add generic stack data structure

I'll want to use this soon enough
---
 schala-lang/src/lib.rs  |  1 +
 schala-lang/src/util.rs | 23 +++++++++++++++++++++++
 2 files changed, 24 insertions(+)
 create mode 100644 schala-lang/src/util.rs

diff --git a/schala-lang/src/lib.rs b/schala-lang/src/lib.rs
index c67e47d..93a8b9d 100644
--- a/schala-lang/src/lib.rs
+++ b/schala-lang/src/lib.rs
@@ -17,6 +17,7 @@ macro_rules! bx {
   ($e:expr) => { Box::new($e) }
 }
 
+mod util;
 mod builtin;
 mod tokenizing;
 mod parsing;
diff --git a/schala-lang/src/util.rs b/schala-lang/src/util.rs
new file mode 100644
index 0000000..2bf46eb
--- /dev/null
+++ b/schala-lang/src/util.rs
@@ -0,0 +1,23 @@
+use std::collections::HashMap;
+use std::hash::Hash;
+use std::cmp::Eq;
+
+#[derive(Default, Debug)]
+pub struct StateStack<'a, T: 'a, V: 'a>  where T: Hash + Eq {
+  parent: Option<&'a StateStack<'a, T, V>>,
+  values: HashMap<T, V>
+}
+
+impl<'a, T, V> StateStack<'a, T, V> where T: Hash + Eq {
+  pub fn insert(&mut self, key: T, value: V) where T: Hash + Eq {
+    self.values.insert(key, value);
+  }
+  pub fn lookup(&self, key: &T) -> Option<&V> where T: Hash + Eq {
+    match (self.values.get(key), self.parent) {
+      (None, None) => None,
+      (None, Some(parent)) => parent.lookup(key),
+      (Some(value), _) => Some(value),
+    }
+  }
+}
+