Add stubbed out type checker

1 files changed, 33 insertions, 0 deletions

diff --git a/src/semantic/environment.rs b/src/semantic/environment.rs
new file mode 100644
index 0000000..fab16b3
--- /dev/null
+++ b/src/semantic/environment.rs
@@ -0,0 +1,33 @@
+use std::collections::HashMap;
+use std::hash::Hash;
+
+pub struct Environment<'a, T: 'a, U: 'a> {
+    pub parent: Option<&'a Environment<'a, T, U>>,
+    pub bindings: HashMap<T, U>,
+}
+
+impl<'a, T: 'a, U: 'a> Environment<'a, T, U>
+    where T: Eq + Hash {
+    pub fn new(parent: Option<&'a Environment<'a, T, U>>) -> Environment<'a, T, U> {
+        Environment {
+            parent: parent,
+            bindings: HashMap::new(),
+        }
+    }
+
+    pub fn add_binding(&mut self, key: T, value: U) {
+        self.bindings.insert(key, value);
+    }
+
+    pub fn lookup(&self, key: &T) -> Option<&U> {
+        if let Some(v) = self.bindings.get(key) {
+            Some(v)
+        }
+        else if let Some(p) = self.parent {
+            p.lookup(key)
+        }
+        else {
+            None
+        }
+    }
+}