Why can't I use "or" here?
in [Ruby]
|
From: botp on 30 Dec 2009 22:36 On Thu, Dec 31, 2009 at 10:24 AM, Albert Schlef <albertschlef(a)gmail.com> wrote: > Why? I thought the only diference between "or" and "||" is the > precedence. yes, so you can do eg >> system "pwd" or raise "no command here" /home/botp => true >> system "asdf" or raise "no command here" RuntimeError: no command here if you know perl, this is no surprise.. as always, there are many ways in ruby, you can use || or the double parens override. happy holiday and best regards -botp
From: Albert Schlef on 31 Dec 2009 00:32 botp wrote: > On Thu, Dec 31, 2009 at 10:24 AM, Albert Schlef <albertschlef(a)gmail.com> > wrote: >> Why? I thought the only diference between "or" and "||" is the >> precedence. > > yes, so you can do eg > >>> system "pwd" or raise "no command here" > /home/botp > => true > >>> system "asdf" or raise "no command here" > RuntimeError: no command here > > if you know perl, this is no surprise.. It *is* a surprise. In Perl, unlike in Ruby, `func(0 or 1)` *does* work.... > > as always, there are many ways in ruby, you can use || or the double > parens override. Well. it turns out there aren't that many ways in ruby. I originally tried to do the following: some_func(ARGV[0] or raise "You must provide an argument") I wish it worked. But it doesn't. So I changed it to: some_func(ARGV[0] || raise "You must provide an argument") It still didn't work. So finally I did: some_func(ARGV[0] || (raise "You must provide an argument")) It works. But, I must say, it isn't as beautiful as my original plan. It doesn't read as English. -- Posted via http://www.ruby-forum.com/.
From: Albert Schlef on 31 Dec 2009 00:39 Albert Schlef wrote: > Well. it turns out there aren't that many ways in ruby. > > I originally tried to do the following: > > some_func(ARGV[0] or raise "You must provide an argument") > > I wish it worked. But it doesn't. So I changed it to: > > some_func(ARGV[0] || raise "You must provide an argument") > > It still didn't work. So finally I did: > > some_func(ARGV[0] || (raise "You must provide an argument")) > > It works. But, I must say, it isn't as beautiful as my original plan. It > doesn't read as English. Hey, I now see that this works: some_func((ARGV[0] or raise "You must provide an argument")) Great. On the other hand, I won't be able to remember this the next time I need it. -- Posted via http://www.ruby-forum.com/.
From: Seebs on 31 Dec 2009 00:29 On 2009-12-31, Albert Schlef <albertschlef(a)gmail.com> wrote: > So it seems Ruby internally recognizes some structures as "statemenets" > and others as "expressions". It seems disapointing at first, but since > Ruby supports precedence for operators (something Lisp doesn't), there > has to be some price to pay. I don't think that's it at all. I think it's that methodname( is a method call (), not a grouping (). Thus the difference between puts(a or b) and puts (a or b) In short, it's nothing to do with statements-vs-expressions, and everything to do with disambiguating method calls vs. parenthesized expressions. -s -- Copyright 2009, all wrongs reversed. Peter Seebach / usenet-nospam(a)seebs.net http://www.seebs.net/log/ <-- lawsuits, religion, and funny pictures http://en.wikipedia.org/wiki/Fair_Game_(Scientology) <-- get educated!
From: Albert Schlef on 31 Dec 2009 01:16
Seebs wrote: > On 2009-12-31, Albert Schlef <albertschlef(a)gmail.com> wrote: >> So it seems Ruby internally recognizes some structures as "statemenets" >> and others as "expressions". It seems disapointing at first, but since >> Ruby supports precedence for operators (something Lisp doesn't), there >> has to be some price to pay. > > I don't think that's it at all. I think it's that methodname( is a > method > call (), not a grouping (). Thus the difference between > puts(a or b) > and > puts (a or b) > > In short, it's nothing to do with statements-vs-expressions, and > everything > to do with disambiguating method calls vs. parenthesized expressions. Interesting. Why is the following a syntax error? puts (123 if true) and the following isn't? puts (123 or 456) -- Posted via http://www.ruby-forum.com/. |