Path: ...!2.eu.feeder.erje.net!feeder.erje.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: "B. Pym" Newsgroups: comp.lang.lisp Subject: Re: Slow Loop (alternatives in lisp?) Date: Mon, 22 Jul 2024 18:29:17 -0000 (UTC) Organization: A noiseless patient Spider Lines: 126 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Injection-Date: Mon, 22 Jul 2024 20:29:17 +0200 (CEST) Injection-Info: dont-email.me; posting-host="9bd2863663604f2e05c19a8ebb644b33"; logging-data="820676"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1860Q3Xw1Vj0rnb8s9mZKUn" User-Agent: XanaNews/1.18.1.6 Cancel-Lock: sha1:J4k+nH+rTwnqxgCNK7/bf01qV50= Bytes: 5076 > * there is already a WHILE in Common Lisp. No need to invent a new one: > > (loop while (foo-p) do .... ) Gauche Scheme (while (read) (print "True enough.")) 2 True enough. #t True enough. 'yes True enough. #f (while (read) => x (print x " is truer than you think.")) "why" why is truer than you think. 88 88 is truer than you think. 0 0 is truer than you think. #f Paul Graham: I consider Loop one of the worst flaws in CL, and an example to be borne in mind by both macro writers and language designers. [In "ANSI Common Lisp", Graham makes the following comments:] The loop macro was originally designed to help inexperienced Lisp users write iterative code. Instead of writing Lisp code, you express your program in a form meant to resemble English, and this is then translated into Lisp. Unfortunately, loop is more like English than its designers ever intended: you can use it in simple cases without quite understanding how it works, but to understand it in the abstract is almost impossible. .... the ANSI standard does not really give a formal specification of its behavior. .... The first thing one notices about the loop macro is that it has syntax. A loop expression contains not subexpressions but clauses. The clauses are not delimited by parentheses; instead, each kind has a distinct syntax. In that, loop resembles traditional Algol-like languages. But the other distinctive feature of loop, which makes it as unlike Algol as Lisp, is that the order in which things happen is only loosely related to the order in which the clauses occur. .... For such reasons, the use of loop cannot be recommended. Dan Weinreb, one of the designers of Common Lisp: .... the problem with LOOP was that it turned out to be hard to predict what it would do, when you started using a lot of different facets of LOOP all together. This is a serious problem since the whole idea of LOOP was to let you use many facets together; if you're not doing that, LOOP is overkill. Barry Margolin: My recommendation is based on seeing many question in the past of the form "What happens if you use both XXX and YYY in the same LOOP?" The unfortunate fact is that when we were writing the standard we didn't have time to nail down all the possible interactions between different LOOP features, so many of these are not well specified. And even if we did get it right in the standard, it's likely to be difficult to find them and I wouldn't trust that all implementors got it right (many of those questions were probably from implementors, trying to figure out what they were supposed to do). And even if they all got it right, someone reading your code may not be able to figure it out. So, with all those potential problems, my feeling is that if you have to ask, it's probably better to use something other than LOOP. > 3. Loop is very powerful, granted, and many people are trying to > argue that "you can do so much with loop that it's unreadable." > This is not an argument. But it is! Because any use of LOOP has the potential to be unreadable, the reader must read it carefully to verify that it's just one of the cases that doesn't require careful reading! John Foderaro: I'm not trying to join a debate on loop. I just wanted to present the other side of [the issue so that] the intelligent people can then weigh the arguments on both sides. I'm not suggesting that loop can be fixed either by adding parenthesis or coming up with ways of indenting it to make it understandable. It's a lost cause. .... Another great example from kmp: === from kmp For example, you might think (loop with i = (random 100) for x from 1 to 10 do (print (list i x))) and (loop for i = (random 100) for x from 1 to 10 do (print (list i x))) meant the same in English, [but they don't do the same thing in loop] === end kmp loop lulls you into thinking that you understand the program since you understand English. Make no mistake about it, loop is its own language. If you use it you condem everyone who reads the code to also learn the loop language.