Made strings indexable

Upsilon/BaseTypes/LuaString.cs

@@ -1,9 +1,10 @@
 using System;
 using Upsilon.BaseTypes.Number;
+using Upsilon.Evaluator;
 
 namespace Upsilon.BaseTypes
 {
-    internal class LuaString : LuaType
+    internal class LuaString : LuaType, IIndexable
     {
         public LuaString(string value)
         {
@@ -76,5 +77,11 @@ namespace Upsilon.BaseTypes
         {
             return Value;
         }
+
+        public LuaType Get(string s, EvaluationScope scope)
+        {
+            var i = int.Parse(s);
+            return new LuaString(Value[i - 1].ToString());
+        }
     }
 }

Upsilon/BaseTypes/LuaTable.cs

@@ -1,7 +1,4 @@
-using System.Collections;
-using System.Collections.Generic;
 using System.Linq;
-using Upsilon.Binder;
 using Upsilon.Evaluator;
 
 namespace Upsilon.BaseTypes

Upsilon/Binder/Binder.cs

@@ -416,15 +416,21 @@ namespace Upsilon.Binder
         private BoundExpression BindIndexExpression(IndexExpressionSyntax e)
         {
             var expression = BindExpression(e.Expression);
-            if (expression.Type != Type.Table && expression.Type != Type.Unknown)
+
+            var index = BindExpression(e.Index);
+            switch (expression.Type)
             {
+                case Type.Table:
+                case Type.UserData:
+                case Type.Unknown:
+                    return new BoundIndexExpression(expression, index, Type.Unknown);
+                case Type.String when index.Type == Type.Number:
+                    return new BoundIndexExpression(expression, index, Type.String);
+                default:
                     //TODO: wrong type diagnostic
                     throw new Exception(expression.Type.ToString());
                     return new BoundLiteralExpression(new LuaNull());
             }
-
-            var index = BindExpression(e.Index);
-            return new BoundIndexExpression(expression, index, Type.Unknown);
         }
     }
 }

UpsilonTests/StringTests.cs

@@ -0,0 +1,51 @@
+using Upsilon.Evaluator;
+using Xunit;
+
+namespace UpsilonTests
+{
+    public class StringTests
+    {
+        [Fact]
+        public void BasicStringVariable()
+        {
+            const string input = @"
+string = ""test""
+return string
+";
+            var script = new Script(input);
+            Assert.Empty(script.Diagnostics.Messages);
+            var evaluated = script.Evaluate<string>();
+            Assert.Empty(script.Diagnostics.Messages);
+            Assert.Equal("test", evaluated);
+        }
+
+        [Fact]
+        public void StringIndexable()
+        {
+            const string input = @"
+string = ""test""
+return string[3]
+";
+            var script = new Script(input);
+            Assert.Empty(script.Diagnostics.Messages);
+            var evaluated = script.Evaluate<string>();
+            Assert.Empty(script.Diagnostics.Messages);
+            Assert.Equal("s", evaluated);
+        }
+
+        [Fact]
+        public void StringAddition()
+        {
+            const string input = @"
+string = ""test"" + ""123""
+return string
+";
+            var script = new Script(input);
+            Assert.Empty(script.Diagnostics.Messages);
+            var evaluated = script.Evaluate<string>();
+            Assert.Empty(script.Diagnostics.Messages);
+            Assert.Equal("test123", evaluated);
+        }
+
+    }
+}