Path: utzoo!utgpu!water!watmath!clyde!bellcore!tness7!killer!pollux!dalsqnt!rpp386!jfh From: jfh@rpp386.UUCP (John F. Haugh II) Newsgroups: comp.lang.c Subject: Re: Unnecessary parenthesis Message-ID: <3863@rpp386.UUCP> Date: 12 Jul 88 05:17:05 GMT References: <326@marob.MASA.COM> <175@lakart.UUCP> <1988Jul10.201845.27751@utzoo.uucp> Reply-To: jfh@rpp386.UUCP (The Beach Bum) Organization: Big "D" Home for Wayward Hackers Lines: 31 In article <1988Jul10.201845.27751@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes: >> ... this is a weakness of RD parsers: the amount of >> work incurred by unnecessary parentheses is quite considerable, especially >> in a language such as C, with 15 levels of operator precedence.... > >Well, yes, *if* you implement the RD parser straight from the grammar and >do no optimization. One can do better, at the price of greater complexity, >by explicitly looking for the simple cases. one of the major strengths of r-d parsers is you can code the parser straight from the grammar. performing the transformations from left to right recursion should be fairly automatic and is the only really worthwhile (ease of coding, speed and complexity tradeoffs being considered) optimization i can see. the geneal case of trying to reduce the recursion present in the parser would seem to require a potentially arbitrary amount of look ahead, or as a minimum, the same amount of lookahead as the length of the shortest sentence the parser is trying to recognize. clarifications, henry? >Anyone who buys Wisconsin cheese is | Henry Spencer @ U of Toronto Zoology >a traitor to mankind. --Pournelle | {ihnp4,decvax,uunet!mnetor}!utzoo!henry and what the hell does this mean??? - john. -- John F. Haugh II +--------- Cute Chocolate Quote --------- HASA, "S" Division | "USENET should not be confused with UUCP: killer!rpp386!jfh | something that matters, like CHOCOLATE" DOMAIN: jfh@rpp386.uucp | -- with my apologizes