Bad error message when block is enclosed in parenthesis

[apblack]

I accidentally used parenthesis instead of braces to enclose a block that has an argument. I get this message

ast.grace[4005:25-30]: Syntax error: an argument list beginning with a '(' must end with a ')'.
4004:     method newVisitImplicit(aNode) -> Done {
4005:         aNode.childrenDo(each -> each.newAccept(self))
------------------------------^^^^^^

The message is not much help because there is indeed a closing ). I believe that the parser sees the ->, notices that it's not a comma or a closing paren, and complains. This case is probably worth a custom error message.