Parse record literals

AST.cs

@@ -1,3 +1,7 @@
 namespace Finn.AST;
 
 public record Name(string Value, bool Quoted);
+
+public record Field(Name Name, Expr? Value);
+
+public record BaseRecord(Expr Value, Field[] Updates);

ASTPrinter.cs

@@ -83,4 +83,46 @@ class ASTPrinter : IVisitor<string>
 		}
 		return parenthesize("variant", new Identifier { Value = expr.Tag }, expr.Argument);
 	}
+
+	public string visitRecordExpr(Record expr)
+	{
+		StringWriter w = new StringWriter();
+		w.Write("(record");
+
+		writeFields("extend", expr.Extensions);
+
+		if (expr.Base != null)
+		{
+			w.Write(" (base ");
+			w.Write(print(expr.Base.Value));
+			writeFields("update", expr.Base.Updates);
+			w.Write(')');
+		}
+		w.Write(')');
+
+		return w.ToString();
+
+		void writeFields(string header, Field[] fields)
+		{
+			if (fields.Length != 0)
+			{
+				w.Write($" ({header}");
+				foreach (var field in fields)
+				{
+					w.Write(' ');
+					var name = formatName(field.Name);
+					if (field.Value == null)
+					{
+						w.Write(name);
+					}
+					else
+					{
+						w.Write(parenthesize(name, field.Value));
+					}
+				}
+				w.Write(')');
+			}
+
+		}
+	}
 }

Expr.g.cs

@@ -20,6 +20,7 @@ public interface IVisitor<T> {
 	T visitIdentifierExpr(Identifier expr);
 	T visitListExpr(List expr);
 	T visitVariantExpr(Variant expr);
+	T visitRecordExpr(Record expr);
 	T visitSelectorExpr(Selector expr);
 }
 public class Sequence : Expr
@@ -101,6 +102,15 @@ public class Variant : Expr
 		return visitor.visitVariantExpr(this);
 	}
 }
+public class Record : Expr
+{
+	public required Field[] Extensions { get; init; }
+	public required BaseRecord? Base { get; init; }
+	public override T accept<T>(IVisitor<T> visitor)
+	{
+		return visitor.visitRecordExpr(this);
+	}
+}
 public class Selector : Expr
 {
 	public required Expr Left { get; init; }

Parser.cs

@@ -44,10 +44,10 @@ class Parser
 		return false;
 	}
 
-	private bool check(TokenType type)
+	private bool check(params TokenType[] types)
 	{
 		if (isAtEnd()) return false;
-		return peek().type == type;
+		return Array.IndexOf(types, peek().type) >= 0;
 	}
 
 	private Token advance()
@@ -327,7 +327,48 @@ class Parser
 
 	private Expr? record()
 	{
-		return null;
+		if (!match(TokenType.LBrace))
-		// TODO record
+		{
+			return null;
+		}
+
+		var extensions = parseFields(TokenType.RBrace, TokenType.Pipe);
+		BaseRecord? baseRecord = null;
+
+		if (match(TokenType.Pipe))
+		{
+			var baseExpr = expression();
+			var updates = match(TokenType.With) ? parseFields(TokenType.RBrace) : Array.Empty<Field>();
+			baseRecord = new(baseExpr, updates);
+		}
+
+		consume(TokenType.RBrace, "Expect '}' at end of record literal.");
+		return new Record
+		{
+			Extensions = extensions,
+			Base = baseRecord,
+		};
+
+		Field[] parseFields(params TokenType[] endAt)
+		{
+			List<Field> fields = new List<Field>();
+
+			while (!check(endAt))
+			{
+				var fieldName = name();
+				if (fieldName == null)
+				{
+					throw error(peek(), "Expect identifier as field name.");
+				}
+				var value = match(TokenType.Equal) ? expression() : null;
+				fields.Add(new(fieldName, value));
+				if (!match(TokenType.Comma))
+				{
+					break;
+				}
+			}
+
+			return fields.ToArray();
+		}
 	}
 }

Program.cs

@@ -39,7 +39,11 @@ class Program
 		Parser parser = new Parser(tokens);
 		Expr? expression = parser.parse();
 
-		if (hadError || expression == null) return;
+		if (hadError || expression == null)
+		{
+			hadError = false;
+			return;
+		}
 
 		Console.WriteLine(new ASTPrinter().print(expression));
 	}

ast_classes.fsx

@@ -28,6 +28,10 @@ let types =
         Fields = [ { Type = "Expr[]"; Name = "Elements" } ] }
       { Name = "Variant"
         Fields = [ { Type = "Name"; Name = "Tag" }; { Type = "Expr?"; Name = "Argument" } ] }
+      { Name = "Record"
+        Fields =
+          [ { Type = "Field[]"; Name = "Extensions" }
+            { Type = "BaseRecord?"; Name = "Base" } ] }
       { Name = "Selector"
         Fields = [ { Type = "Expr"; Name = "Left" }; { Type = "Name"; Name = "FieldName" } ] } ]