Lots of work on type binding

Upsilon/Binder/BoundScope.cs

@@ -0,0 +1,51 @@
+using System.Collections.Generic;
+
+namespace Upsilon.Binder
+{
+    public class BoundScope
+    {
+        private readonly BoundScope _parentScope;
+        private readonly Dictionary<string, VariableSymbol> _variables;
+
+        public BoundScope(BoundScope parentScope)
+        {
+            _parentScope = parentScope;
+            _variables = new Dictionary<string, VariableSymbol>();
+        }
+
+        public void SetVariable(VariableSymbol var)
+        {
+            if (_variables.ContainsKey(var.Name))
+                _variables[var.Name] = var;
+            else
+                _variables.Add(var.Name, var);
+        }
+
+        public void SetGlobalVariable(VariableSymbol var)
+        {
+            if (_parentScope == null)
+            {
+                SetVariable(var);
+            }
+            else
+            {
+                _parentScope.SetGlobalVariable(var);
+            }
+        }
+
+
+        public bool TryGetVariable(string key, out VariableSymbol result)
+        {
+            if (_variables.TryGetValue(key, out result))
+            {
+                return true;
+            }
+            if (_parentScope != null)
+            {
+                return _parentScope.TryGetVariable(key, out result);
+            }
+            return false;
+        }
+
+    }
+}