> And of course the actual place where nastiness happens is the user input, and I haven't yet seen a place that can statically typecheck users. ;-) User input

> And of course the actual place where nastiness happens is the user input, and I haven't yet seen a place that can statically typecheck users. ;-) User input has type `ByteString`. Not only can we check that statically, we absolutely should; and we should enforce that type, to reject any code which assumes otherwise. Nastiness happens when developers treat user input as something other than ByteString; e.g. they might try appending it to a fragment of HTML (XSS); or wrap it in quotation marks and send it to a database (SQL injection). We don't need to 'statically typecheck users'; we do need to statically check that `myApp` has type `ByteString -> Foo`, so we can avoid ever executing implementations which actually have type `HTMLFragment -> Foo` (XSS), or `SQLFragment -> Foo` (SQL injection), or whatever.