Adds Nil

Upsilon/BaseTypes/LuaNull.cs

@@ -0,0 +1,12 @@
+namespace Upsilon.BaseTypes
+{
+    public class LuaNull : LuaType
+    {
+        public override Type Type => Type.Nil;
+
+        public override string ToString()
+        {
+            return "null";
+        }
+    }
+}

Upsilon/Binder/Binder.cs

@@ -110,11 +110,15 @@ namespace Upsilon.Binder
                     type = Type.Boolean;
                     outValue = new LuaBoolean(b);
                     break;
+                case null:
+                    type     = Type.Nil;
+                    outValue = new LuaNull();
+                    break;
                 default:
                     _diagnostics.LogUnknownType(e.Span);
                     break;
             }
-            return new BoundLiteralExpression(outValue, type);
+            return new BoundLiteralExpression(outValue);
         }
 
         private BoundExpression BindParenthesizedExpression(ParenthesizedExpressionSyntax e)
@@ -128,7 +132,7 @@ namespace Upsilon.Binder
             if (!_scope.TryGetVariable(name, out var variable))
             {
                 _diagnostics.LogUnknownVariable(e.Identifier.Span, name);
-                return new BoundLiteralExpression(null, Type.Nil);
+                return new BoundLiteralExpression(new LuaNull());
             }
 
             return new BoundVariableExpression(variable);

Upsilon/Binder/BoundExpressions/BoundLiteralExpression.cs

@@ -4,14 +4,13 @@ namespace Upsilon.Binder
 {
     public class BoundLiteralExpression : BoundExpression
     {
-        public BoundLiteralExpression(LuaType value, Type type)
+        public BoundLiteralExpression(LuaType value)
         {
             Value = value;
-            Type = type;
         }
 
         public override BoundKind Kind => BoundKind.BoundLiteralExpression;
-        public override Type Type { get; }
+        public override Type Type => Value.Type;
         public LuaType Value { get; }
     }
 }

Upsilon/Parser/Parser.cs

@@ -181,6 +181,9 @@ namespace Upsilon.Parser
                 case SyntaxKind.Identifier:
                     var token = MatchToken(SyntaxKind.Identifier);
                     return new VariableExpressionSyntax((IdentifierToken) token);
+                case SyntaxKind.NilKeyword:
+                    var nilToken = MatchToken(SyntaxKind.NilKeyword);
+                    return new LiteralExpressionSyntax(nilToken, null);
                 default:
                     _diagnostics.LogBadCharacter(new TextSpan(_position, 1), SyntaxKind.Identifier);
                     NextToken();

Upsilon/Parser/SyntaxKeyWords.cs

@@ -28,6 +28,8 @@ namespace Upsilon.Parser
                     return SyntaxKind.ElseIfKeyword;
                 case "else":
                     return SyntaxKind.ElseKeyword;
+                case "nil":
+                    return SyntaxKind.NilKeyword;
                 default:
                     return SyntaxKind.Identifier;
             }

Upsilon/Parser/SyntaxKind.cs

@@ -32,6 +32,7 @@ namespace Upsilon.Parser
         ThenKeyword,
         ElseIfKeyword,
         ElseKeyword,
+        NilKeyword,
 
         Identifier,
 
@@ -52,6 +53,6 @@ namespace Upsilon.Parser
         BlockStatement,
         IfStatement,
         ElseIfStatement,
-        ElseStatement
+        ElseStatement,
     }
 }