for in syntax

compiler/NubLang/Syntax/Parser.cs

@@ -241,6 +241,8 @@ public sealed class Parser
                     return ParseIf(startIndex);
                 case Symbol.While:
                     return ParseWhile(startIndex);
+                case Symbol.For:
+                    return ParseFor(startIndex);
                 case Symbol.Let:
                     return ParseVariableDeclaration(startIndex);
                 case Symbol.Defer:
@@ -330,6 +332,23 @@ public sealed class Parser
         return new WhileSyntax(GetTokens(startIndex), condition, body);
     }
 
+    private ForSyntax ParseFor(int startIndex)
+    {
+        var itemName = ExpectIdentifier().Value;
+        string? indexName = null;
+
+        if (TryExpectSymbol(Symbol.Comma))
+        {
+            indexName = ExpectIdentifier().Value;
+        }
+
+        ExpectSymbol(Symbol.In);
+        var target = ParseExpression();
+        var body = ParseBlock();
+
+        return new ForSyntax(GetTokens(startIndex), itemName, indexName, target, body);
+    }
+
     private ExpressionSyntax ParseExpression(int precedence = 0)
     {
         var startIndex = _tokenIndex;