Parser speed is negligible contributor to slowness in any compiler. rustc has a couple of places were it performs bounded lookahead to supply suggestions for in

Parser speed is negligible contributor to slowness in any compiler. rustc has a couple of places were it performs bounded lookahead to supply suggestions for incorrect code, but the grammar of the language is regular. 3rd party tools don't have to worry about it, and users get accurate suggestions. The cost is 1) you have to implement a more complex parser while 2) making people go "you already know what I meant, just take it without me using the 'ugly' turbofish". It think this is the correct approach for language design.