# Elsunless: Compiles but does not run. Standard? **URL:** \ **Category:** ruby-talk\ **Created:** [12 March 2008 14:19 UTC](https://rubytalk.org/t/elsunless-compiles-but-does-not-run-standard/45120 "2008-03-12T14:19:49Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![Fred\_Talpiot](https://avatars.discourse-cdn.com/v4/letter/f/7ea924/32.png) [@Fred\_Talpiot](https://rubytalk.org/u/Fred_Talpiot)\ **Post date:** [12 March 2008 14:19 UTC](https://rubytalk.org/t/elsunless-compiles-but-does-not-run-standard/45120/1 "2008-03-12T14:19:49Z")
In Ruby: 1) 'if' can be followed by 'elsif'. 2) 'unless' can NOT be followed by 'elsif'. It gets a syntax error. 3) 'unless' can be followed by 'elsunless', but it does not run okay. 3a) 'if' can also be followed by 'elsunless', with the same dismal results. 4) So what's the standard? 5) The following code: > **···** > > ------------------- > puts 'ruby version: ' + RUBY\_VERSION + ', ' + RUBY\_RELEASE\_DATE + ' for > ' + RUBY\_PLATFORM > > unless true >   puts "wrong wrong" > elsunless false >   puts 'weird, but logical' > elsunless true >   puts 'truly strange' > else >   puts 'weirder yet' # This is what pops out! > end > > # and 'elsif' is a syntax error following 'unless' > ------------------- > Produces the following on WinXP: > > > ruby unless.rb > > ruby version: 1.8.6, 2007-09-24 for i386-mswin32 > weirder yet > > And, on Linux: > > $ ruby unless.rb > ruby version: 1.8.6, 2007-09-24 for x86\_64-linux > weirder yet > > We can be sure this behavior is not as intended. We cannot be sure > exactly what was intended. > > The following rule is from the wiki reference page: > [http://en.wikibooks.org/wiki/Ruby\_Programming/Syntax/Control\_Structures#unless](http://en.wikibooks.org/wiki/Ruby_Programming/Syntax/Control_Structures#unless) > >   \>The unless expression is treated exactly like a negated if > expression: >   \> >   \> if !expression # is equal to using >   \> unless expression > > Obviously, that rule is not being followed. If it were, the 'elsif' > would > be permitted. > > The interpreter has a bug. The documentation may also be wrong, hard to > know for sure... > > name already taken > -- > Posted via [http://www.ruby-forum.com/\](http://www.ruby-forum.com/%5C). ---
**Author:** ![Peter\_Hickman](https://avatars.discourse-cdn.com/v4/letter/p/ecd19e/32.png) [@Peter\_Hickman](https://rubytalk.org/u/Peter_Hickman)\ **Post date:** [12 March 2008 14:31 UTC](https://rubytalk.org/t/elsunless-compiles-but-does-not-run-standard/45120/2 "2008-03-12T14:31:08Z")
Are you sure about this. I am getting: fred.rb:4:in `x': undefined method `elsunless' for main:Object (NoMethodError) I think that there is no such thing as elsunless. How about some more realistic test code? ---
**Author:** ![Nobuyoshi\_Nakada1](https://avatars.discourse-cdn.com/v4/letter/n/9f8e36/32.png) [@Nobuyoshi\_Nakada1](https://rubytalk.org/u/Nobuyoshi_Nakada1)\ **Post date:** [12 March 2008 14:32 UTC](https://rubytalk.org/t/elsunless-compiles-but-does-not-run-standard/45120/3 "2008-03-12T14:32:19Z")
Hi, At Wed, 12 Mar 2008 23:19:49 +0900, Fred Talpiot wrote in [ruby-talk:294281]: > 3) 'unless' can be followed by 'elsunless', but it does not run okay. > 3a) 'if' can also be followed by 'elsunless', with the same dismal > results. No such keyword. > unless true >   puts "wrong wrong" > elsunless false This is assumed a method call, but not reached. > **···** > > -- > Nobu Nakada ---
**Author:** ![Stefan\_Lang1](https://avatars.discourse-cdn.com/v4/letter/s/46a35a/32.png) [@Stefan\_Lang1](https://rubytalk.org/u/Stefan_Lang1)\ **Post date:** [12 March 2008 14:43 UTC](https://rubytalk.org/t/elsunless-compiles-but-does-not-run-standard/45120/4 "2008-03-12T14:43:07Z")
elsunless is not a keyword in Ruby. Let's reformat your code a little bit:     unless true       puts "wrong wrong"       elsunless false       puts 'weird, but logical'       elsunless true       puts 'truly strange'       else       puts 'weirder yet' # This is what pops out!     end Syntax wise, Ruby sees the "elsunless" occurences here as plain method calls. Since the unless condition is true, the whole block gets never executed and there's no exception. Let's compare in irb:     irb(main):001:0\> elsif true     SyntaxError: compile error     (irb):1: syntax error, unexpected kELSIF     elsif true          ^             from (irb):1     irb(main):002:0\> elsunless true     NoMethodError: undefined method `elsunless' for main:Object             from (irb):2 Stefan > **···** > > 2008/3/12, Fred Talpiot \: > > > [...] > > puts 'ruby version: ' + RUBY\_VERSION + ', ' + RUBY\_RELEASE\_DATE + ' for > > ' + RUBY\_PLATFORM > > > > unless true > >   puts "wrong wrong" > > elsunless false > >   puts 'weird, but logical' > > elsunless true > >   puts 'truly strange' > > else > >   puts 'weirder yet' # This is what pops out! > > end ---
**Author:** ![Thomas\_Wieczorek](https://avatars.discourse-cdn.com/v4/letter/t/e47c2d/32.png) [@Thomas\_Wieczorek](https://rubytalk.org/u/Thomas_Wieczorek)\ **Post date:** [12 March 2008 14:45 UTC](https://rubytalk.org/t/elsunless-compiles-but-does-not-run-standard/45120/5 "2008-03-12T14:45:28Z")
Ruby is an interpreted language, so it ignores your "unless true" part and doesn't parse what's after it until the "else". Your code should look like that: unless true     puts "wrong wrong"     elsunless false     puts 'weird, but logical'     elsunless true     puts 'truly strange' else     puts 'weirder yet' # This is what pops out! end Nobu is right. Try "unless false" instead of "unless true" and you'll get a NameError > **···** > > On Wed, Mar 12, 2008 at 3:19 PM, Fred Talpiot \ wrote: > > > unless true > >   puts "wrong wrong" > > elsunless false > >   puts 'weird, but logical' > > elsunless true > >   puts 'truly strange' > > else > >   puts 'weirder yet' # This is what pops out! > > end ---
**Author:** ![Stefan\_Lang1](https://avatars.discourse-cdn.com/v4/letter/s/46a35a/32.png) [@Stefan\_Lang1](https://rubytalk.org/u/Stefan_Lang1)\ **Post date:** [12 March 2008 15:15 UTC](https://rubytalk.org/t/elsunless-compiles-but-does-not-run-standard/45120/6 "2008-03-12T15:15:07Z")
Damn, the "else" should not be indented. Stefan > **···** > > 2008/3/12, Stefan Lang \: > > > elsunless is not a keyword in Ruby. Let's reformat your > > code a little bit: > > > >     unless true > >       puts "wrong wrong" > >       elsunless false > >       puts 'weird, but logical' > >       elsunless true > >       puts 'truly strange' > >       else > >       puts 'weirder yet' # This is what pops out! > >     end ---
**Author:** ![Fred\_Talpiot](https://avatars.discourse-cdn.com/v4/letter/f/7ea924/32.png) [@Fred\_Talpiot](https://rubytalk.org/u/Fred_Talpiot)\ **Post date:** [12 March 2008 16:27 UTC](https://rubytalk.org/t/elsunless-compiles-but-does-not-run-standard/45120/7 "2008-03-12T16:27:05Z")
Yup, you guys were right about ONE thing, the 'elsunless' was not being parsed. It ain't a keyword. It ain't nuthin'. BUT the 'unless ... elsif' sequence SHOULD be accepted, if the wiki is right. The wiki claims that 'unless X' is the same as 'if ! X'. And that is NOT true with regard to 'elsif'. name already taken > **···** > > -- > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/). ---
**Author:** ![Stefan\_Lang1](https://avatars.discourse-cdn.com/v4/letter/s/46a35a/32.png) [@Stefan\_Lang1](https://rubytalk.org/u/Stefan_Lang1)\ **Post date:** [12 March 2008 16:55 UTC](https://rubytalk.org/t/elsunless-compiles-but-does-not-run-standard/45120/8 "2008-03-12T16:55:46Z")
The wiki first describes the plain if expression - without else or elsif. Then it describes unless and says it's the opposite of if. And only afterwards comes the description of else and elsif. Makes sense to me. But it's a wiki and you're invited to improve it if you think it needs clarification. (Well, and I'd find it ugly if Ruby actually allowed and elsif in an unless.) Stefan > **···** > > 2008/3/12, Fred Talpiot \: > > > Yup, you guys were right about ONE thing, the 'elsunless' was > > not being parsed. It ain't a keyword. It ain't nuthin'. > > > > BUT the 'unless ... elsif' sequence SHOULD be accepted, if the > > wiki is right. The wiki claims that 'unless X' is the same as > > 'if ! X'. And that is NOT true with regard to 'elsif'. ---
**Author:** ![Lionel\_Bouton](https://avatars.discourse-cdn.com/v4/letter/l/a88e4f/32.png) [@Lionel\_Bouton](https://rubytalk.org/u/Lionel_Bouton)\ **Post date:** [12 March 2008 17:15 UTC](https://rubytalk.org/t/elsunless-compiles-but-does-not-run-standard/45120/9 "2008-03-12T17:15:05Z")
Fred Talpiot wrote: > Yup, you guys were right about ONE thing, the 'elsunless' was > not being parsed. It ain't a keyword. It ain't nuthin'. > > BUT the 'unless ... elsif' sequence SHOULD be accepted, if the > wiki is right. Why should we care about this wiki? There are thousands of ressources on Ruby. If you want to fix them when they aren't reliable enough, you are welcomed to do so but I don't see what you expect us to do with imaginary elsunless and elsif keywords in the unless constructs. Lionel ---
**Author:** ![Fred\_Talpiot](https://avatars.discourse-cdn.com/v4/letter/f/7ea924/32.png) [@Fred\_Talpiot](https://rubytalk.org/u/Fred_Talpiot)\ **Post date:** [13 March 2008 11:44 UTC](https://rubytalk.org/t/elsunless-compiles-but-does-not-run-standard/45120/10 "2008-03-13T11:44:46Z")
Lionel: I never meant you had to do anything, I was asking about the standard. Why the Wiki? I went to [http://www.ruby-lang.org/en/documentation/](http://www.ruby-lang.org/en/documentation/) and started looking down the page for a 'language reference'. The wiki is the only one described on that page as a 'reference' to the language. The rest of the references there are to the libraries. > **···** > > -- > Posted via [http://www.ruby-forum.com/](http://www.ruby-forum.com/).