Parse record patterns

AST.cs

@@ -61,3 +61,11 @@ public partial record Let
 		return $"Let {{ Bindings = {string.Join(", ", (IEnumerable<object?>)(this.Bindings))}, Body = {this.Body} }}";
 	}
 }
+
+public partial record RecordPattern
+{
+	public override string ToString()
+	{
+		return $"Let {{ Bindings = {string.Join(", ", (IEnumerable<object?>)(this.Fields))}, Rest = {this.Rest} }}";
+	}
+}

Parser.cs

@@ -167,7 +167,25 @@ class Parser
 		{
 			return null;
 		}
-		throw new NotImplementedException("TODO record pattern");
+
+		List<FieldPattern> fields = new List<FieldPattern>();
+		while (!check(TokenType.RBrace, TokenType.Pipe))
+		{
+			var fieldName = name();
+			if (fieldName == null)
+			{
+				throw error(peek(), "Expect identifier as field name.");
+			}
+			var pat = match(TokenType.Equal) ? pattern() : null;
+			fields.Add(new(fieldName, pat));
+			if (!match(TokenType.Comma))
+			{
+				break;
+			}
+		}
+		var restPattern = match(TokenType.Pipe) ? simplePattern() : null;
+		consume(TokenType.RBrace, "Expect '}' at end of record pattern.");
+		return new(fields.ToArray(), restPattern);
 	}
 
 	private VariantPattern? variantPattern()
@@ -190,7 +208,7 @@ class Parser
 		return new(tag, argument);
 	}
 
-	private Pattern pattern()
+	private SimplePattern? simplePattern()
 	{
 		if (match(TokenType.Blank))
 		{
@@ -203,8 +221,17 @@ class Parser
 			return new SimplePattern(identifier);
 		}
 
-		Pattern? p = recordPattern();
-		if (p != null)
+		return null;
+	}
+
+	private Pattern pattern()
+	{
+		Pattern? p;
+		if ((p = simplePattern()) != null)
+		{
+			return p;
+		}
+		if ((p = recordPattern()) != null)
 		{
 			return p;
 		}
@@ -212,7 +239,15 @@ class Parser
 		{
 			return p;
 		}
-		throw error(peek(), "Expect pattern after 'let'.");
+		if (check(TokenType.String))
+		{
+			throw error(peek(), "Cannot pattern-match string literals.");
+		}
+		if (check(TokenType.Number))
+		{
+			throw error(peek(), "Cannot pattern-match numbers.");
+		}
+		throw error(peek(), "Expect pattern.");
 	}
 
 	private Expr let()