# Ruby Whitespace Semantics **URL:** \ **Category:** Ruby\ **Created:** [February 27, 2006, 8:45am UTC](https://www.ruby-forum.com/t/ruby-whitespace-semantics/54234 "2006-02-27T08:45:58Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Almann\_G](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac8455/32.png) [@Almann\_G](https://www.ruby-forum.com/u/Almann_G)\ **Post date:** [February 27, 2006, 8:45am UTC](https://www.ruby-forum.com/t/ruby-whitespace-semantics/54234/1 "2006-02-27T08:45:58Z")
Can someone please explain the semantics behind the following: irb(main):001:0\> a = ( 4 + 5 ) =\> 9 irb(main):002:0\> a = ( 4 irb(main):003:1\> + 5 ) =\> 5 irb(main):004:0\> a = ( 4 + irb(main):005:1\* 5 ) =\> 9 The first and last statements make sense to me, but why is the second one returning 5? I find semantics like this troubling, and no documentation sheds light as to what would cause this behavior. Thanks, Almann ---
**Author:** ![Almann\_G](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac8455/32.png) [@Almann\_G](https://www.ruby-forum.com/u/Almann_G)\ **Post date:** [February 27, 2006, 8:55am UTC](https://www.ruby-forum.com/t/ruby-whitespace-semantics/54234/2 "2006-02-27T08:55:05Z")
Almann G. wrote: > The first and last statements make sense to me, but why is the second one > returning 5? > > I find semantics like this troubling, and no documentation sheds light as > to what would cause this behavior. I understand your concern. Let me try to clarify. Expressions in Ruby can be like standalone statements. Statements are terminated with an optional semicolon or with a newline. If a statement is incomplete, it is understood to go on to the next line; if it is complete, it is just as if terminated with a semicolon. Therefore: a = (4 +5) is the same as a = (4; +5) or even a = (4; +5) That is, it evaluates a “4” and then evaluates a “+5” (which then is the resultant value, as it was the last evaluated). But with a = (4+ 5) the parser is able to see that the expression is not complete, and is apparently continued on the next line. ---
**Author:** ![Almann\_G](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac8455/32.png) [@Almann\_G](https://www.ruby-forum.com/u/Almann_G)\ **Post date:** [February 27, 2006, 8:55am UTC](https://www.ruby-forum.com/t/ruby-whitespace-semantics/54234/3 "2006-02-27T08:55:06Z")
Almann G. wrote: > I’m no expert, but I think it has to do with both first and third having the + operator on the first line and the second one having the + operator on the second line - note also that irb understands that the third case is a continuation of the previous line (_), but the second case is treated almost as 2 separate statements - no (_). I’m sure someone else will have a better idea Kev ---
**Author:** ![Almann\_G](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac8455/32.png) [@Almann\_G](https://www.ruby-forum.com/u/Almann_G)\ **Post date:** [February 27, 2006, 10:26am UTC](https://www.ruby-forum.com/t/ruby-whitespace-semantics/54234/4 "2006-02-27T10:26:16Z")
> =\> 9 > > The first and last statements make sense to me, but why is the second one > returning 5? > > I find semantics like this troubling, and no documentation sheds light as > to what would cause this behavior. > This behaviour is documented, at least here: > [http://www.rubycentral.com/book/language.html](http://www.rubycentral.com/book/language.html) and probably in other placess too (but I wouldn’t know about them as I am learning Ruby for just a little more than 1 week). Hope it helps, Alex ---
**Author:** ![Almann\_G](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac8455/32.png) [@Almann\_G](https://www.ruby-forum.com/u/Almann_G)\ **Post date:** [February 27, 2006, 9:19am UTC](https://www.ruby-forum.com/t/ruby-whitespace-semantics/54234/5 "2006-02-27T09:19:25Z")
Thanks, the semantic is clearer now even though I think it is very clumsy. As an aside, it is interesting that Ruby allows for suites of statements to be used in a grouping context (the parenthesis)–most other languages that are whitespace sensitive don’t allow this since it gets confusing with expressions (as my example shows). -Almann ---
**Author:** ![Almann\_G](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac8455/32.png) [@Almann\_G](https://www.ruby-forum.com/u/Almann_G)\ **Post date:** [February 27, 2006, 5:42pm UTC](https://www.ruby-forum.com/t/ruby-whitespace-semantics/54234/6 "2006-02-27T17:42:24Z")
Quoting Almann G. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > The first and last statements make sense to me, but why is the > second one returning 5? a = ( 4 + 5 ) a = ( 4 ; + 5 ) a = ( 4 + 5 ) A line break begins a new statement unless there is a dangling binary operator or line continuation. -mental ---
**Author:** ![Almann\_G](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac8455/32.png) [@Almann\_G](https://www.ruby-forum.com/u/Almann_G)\ **Post date:** [February 27, 2006, 4:25pm UTC](https://www.ruby-forum.com/t/ruby-whitespace-semantics/54234/7 "2006-02-27T16:25:41Z")
This behavior actually isn’t well documented, since the semantic is unclear in that documentation (or the Ruby Manual) what will happen in the case that the grouping operator is used in this manner. In a nutshell, newline delimits statements except when it doesn’t (trail with a binary operator for instance)… not a really good semantic but I’ll add that to the list of gotchas I need to deal with in Ruby. The 1.4 English Ruby Manual says: Each expression are delimited by semicolons(😉 or newlines. The current Japanese Ruby Manual essentially says the same thing (my Japanese isn’t as sharp as it used to be): 式と式のé??はã?»ã??ã?³ã?­ã?³(;)まã?はæ?¹è¡?でå?ºå??ã??まã? (shiki to shiki no aida wa semikoron(😉 mata wa kaigyou de kugirimasu) -Almann ---
**Author:** ![Almann\_G](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac8455/32.png) [@Almann\_G](https://www.ruby-forum.com/u/Almann_G)\ **Post date:** [February 27, 2006, 6:16pm UTC](https://www.ruby-forum.com/t/ruby-whitespace-semantics/54234/8 "2006-02-27T18:16:24Z")
It is generally good coding style in any programming language, when continuing an expression across more than one line, to split the lines after an operator or other punctuation symbol which indicates that the expression is unfinished. I.e. ``` somefunction( ...very long argument list, more arguments) ``` or (4 + 5) This gives the reader a visual hint that the expression is incomplete, and continues onto the next line. Ruby just uses the same heuristic that a human reader would use. ~Avdi ---
**Author:** ![Almann\_G](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac8455/32.png) [@Almann\_G](https://www.ruby-forum.com/u/Almann_G)\ **Post date:** [February 27, 2006, 8:04pm UTC](https://www.ruby-forum.com/t/ruby-whitespace-semantics/54234/9 "2006-02-27T20:04:15Z")
On 2/27/06, Mark W. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > is the same as > > > > a = (4; > > +5) > > But (4 is clearly an incomplete statement. Actually, notice the semicolon. What Hal is demonstrating is that a parenthetical group can contain multiple expressions. The newline terminates the expression ‘4’, which is a complete expression, while the statement (which happens to include that expression) is continued on the next line. Jacob F. ---
**Author:** ![Almann\_G](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac8455/32.png) [@Almann\_G](https://www.ruby-forum.com/u/Almann_G)\ **Post date:** [February 27, 2006, 8:01pm UTC](https://www.ruby-forum.com/t/ruby-whitespace-semantics/54234/10 "2006-02-27T20:01:12Z")
“Hal F.” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote in message news:removed\_email\_address@domain.invalid… > is the same as > > a = (4; > +5) But (4 is clearly an incomplete statement. ---
**Author:** ![Almann\_G](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac8455/32.png) [@Almann\_G](https://www.ruby-forum.com/u/Almann_G)\ **Post date:** [February 27, 2006, 8:50pm UTC](https://www.ruby-forum.com/t/ruby-whitespace-semantics/54234/11 "2006-02-27T20:50:33Z")
You’re not alone. I’ve adopted this practice in C programs ever since I read about it in a book called _Human Factors and Typography for More Readable Programs_, by Ronald M. Baeker and Aaron Markus, ACM Press, 1990. The authors recommend breaking long lines at operators “of relatively low precedence” and placing the operator at the beginning of the second line because “it emphasizes at the beginning of the continuation that the second line is a continuation.” ---
**Author:** ![Almann\_G](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac8455/32.png) [@Almann\_G](https://www.ruby-forum.com/u/Almann_G)\ **Post date:** [February 27, 2006, 8:56pm UTC](https://www.ruby-forum.com/t/ruby-whitespace-semantics/54234/12 "2006-02-27T20:56:50Z")
Quoting Anthony DeRobertis [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > Well, when I work in languages other than Ruby (not in ruby, of > course, because its a syntax error), I’ve always found: > > foo = a + b + c … > + z > > more readable myself, but I’m probably just a weirdo. It works fine in Ruby if you use a backslash to continue the statement: foo = a + b + c + z -mental ---
**Author:** ![Almann\_G](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac8455/32.png) [@Almann\_G](https://www.ruby-forum.com/u/Almann_G)\ **Post date:** [February 27, 2006, 10:50pm UTC](https://www.ruby-forum.com/t/ruby-whitespace-semantics/54234/13 "2006-02-27T22:50:02Z")
Ah. I thought a semicolon terminated a statement. ---
**Author:** ![Almann\_G](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac8455/32.png) [@Almann\_G](https://www.ruby-forum.com/u/Almann_G)\ **Post date:** [February 27, 2006, 8:22pm UTC](https://www.ruby-forum.com/t/ruby-whitespace-semantics/54234/14 "2006-02-27T20:22:46Z")
Avdi G. wrote: > (4 + > 5) > > This gives the reader a visual hint that the expression is incomplete, > and > continues onto the next line. Ruby just uses the same heuristic that > a human reader would use. Well, when I work in languages other than Ruby (not in ruby, of course, because its a syntax error), I’ve always found: foo = a + b + c … + z more readable myself, but I’m probably just a weirdo. ---
**Author:** ![Almann\_G](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac8455/32.png) [@Almann\_G](https://www.ruby-forum.com/u/Almann_G)\ **Post date:** [February 27, 2006, 11:14pm UTC](https://www.ruby-forum.com/t/ruby-whitespace-semantics/54234/15 "2006-02-27T23:14:33Z")
It does. 4 is a valid statement in Ruby. Ruby doesn’t have the same sharp division as many other languages. 4 is a statement, 4 + 5 is a statement, and +5 is a statement. The return value of a series of statements is the value of the final statement. As a result, the value of ‘4; +5’ is 5. ---
**Author:** ![Almann\_G](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac8455/32.png) [@Almann\_G](https://www.ruby-forum.com/u/Almann_G)\ **Post date:** [February 27, 2006, 11:02pm UTC](https://www.ruby-forum.com/t/ruby-whitespace-semantics/54234/16 "2006-02-27T23:02:17Z")
Quoting removed\_email\_address@domain.invalid: > Ah. I thought a semicolon terminated a statement. It does; it’s just that the current Ruby grammar permits multiple statements within the same set of parenthesis (separated by semicolons or newlines). -mental ---
**Author:** ![Almann\_G](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac8455/32.png) [@Almann\_G](https://www.ruby-forum.com/u/Almann_G)\ **Post date:** [February 27, 2006, 11:33pm UTC](https://www.ruby-forum.com/t/ruby-whitespace-semantics/54234/17 "2006-02-27T23:33:20Z")
On Tue, Feb 28, 2006 at 04:21:02AM +0900, Anthony DeRobertis wrote: > (…) > Well, when I work in languages other than Ruby (not in ruby, of course, > because its a syntax error), I’ve always found: > > foo = a + b + c … > + z If this is M(atlab) then the three dots serve to signal that the line is continued, i.e. serving the same purpose as does \ in ruby. I.e. you’re explicitely stating already that the expression continues on next line (just as you would by adding a \ or ). -m ---
**Author:** ![Almann\_G](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac8455/32.png) [@Almann\_G](https://www.ruby-forum.com/u/Almann_G)\ **Post date:** [February 27, 2006, 11:45pm UTC](https://www.ruby-forum.com/t/ruby-whitespace-semantics/54234/18 "2006-02-27T23:45:37Z")
Quoting Timothy G. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > It does. 4 is a valid statement in Ruby. Ruby doesn’t have the > same sharp division as many other languages. Well… not really. There’s the same distinction in Ruby too (see expr versus compstmt in parse.y). It’s more that Ruby’s grammar permits statement lists in places that many other languages only permit expressions (like inbetween parenthesis). -mental ---
**Author:** ![Almann\_G](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac8455/32.png) [@Almann\_G](https://www.ruby-forum.com/u/Almann_G)\ **Post date:** [February 28, 2006, 4:20pm UTC](https://www.ruby-forum.com/t/ruby-whitespace-semantics/54234/19 "2006-02-28T16:20:43Z")
Martin S. Weber wrote: > On Tue, Feb 28, 2006 at 04:21:02AM +0900, Anthony DeRobertis wrote: > > foo = a + b + c … > > + z > > If this is M(atlab) then the three dots serve to signal > that the line is continued, i.e. serving the same purpose > as does \ in ruby. No, that’s pseudo-code and the three dots are an ellipsis indicating elided material. Yeah, sure, it should have been U+2026 (â?¦) â?? but I’m lazy. ---
**Author:** ![Almann\_G](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/ac8455/32.png) [@Almann\_G](https://www.ruby-forum.com/u/Almann_G)\ **Post date:** [February 28, 2006, 5:07pm UTC](https://www.ruby-forum.com/t/ruby-whitespace-semantics/54234/20 "2006-02-28T17:07:10Z")
On Wed, Mar 01, 2006 at 12:18:20AM +0900, Anthony DeRobertis wrote: > No, that’s pseudo-code and the three dots are an ellipsis indicating > elided material. Yeah, sure, it should have been U+2026 (?) ? but I’m > lazy. _snore_ Sorry 🙂 -Martin [Next page](https://www.ruby-forum.com/t/ruby-whitespace-semantics/54234.md?page=2)