ruby-1.9.2-p0 > 2 + sqrt 5 SyntaxError: (irb):25: syntax error, unexpected tINTEGER, expecting keyword_do or '{' or '(' from /home/martin/.rvm/rubies/ruby-1.9.2-p0/bin/irb:17:in `<main>' I can't see why that doesn't parse properly. martin

on 2011-10-11 09:55

on 2011-10-11 11:19

On Tue, Oct 11, 2011 at 9:54 AM, Martin DeMello <martindemello@gmail.com>wrote: > ruby-1.9.2-p0 > 2 + sqrt 5 > SyntaxError: (irb):25: syntax error, unexpected tINTEGER, expecting > keyword_do or '{' or '(' > from /home/martin/.rvm/rubies/ruby-1.9.2-p0/bin/irb:17:in `<main>' > > I can't see why that doesn't parse properly. > > In 1.8.7 I get the following: irb(main):011:0> 2 + sqrt 5 SyntaxError: compile error (irb):11: syntax error, unexpected tINTEGER, expecting kDO or '{' or '(' from (irb):11 from :0 but this one works irb(main):014:0> 2 + Math.sqrt(5) => 4.23606797749979

on 2011-10-11 12:33

On Oct 11, 2011, at 2:54 AM, Martin DeMello wrote: > ruby-1.9.2-p0 > 2 + sqrt 5 > SyntaxError: (irb):25: syntax error, unexpected tINTEGER, expecting > keyword_do or '{' or '(' > from /home/martin/.rvm/rubies/ruby-1.9.2-p0/bin/irb:17:in `<main>' > > I can't see why that doesn't parse properly. > > martin > You have two options. First, you can tell ruby what library it needs to load (in this case the Math library), or you can include it. You also have to surround your number in parentheses (). This means your code would either look like this: ruby-1.9.2-p290 :004 > 2 + Math.sqrt(5) => 4.23606797749979 OR ruby-1.9.2-p290 :005 > include Math => Object ruby-1.9.2-p290 :006 > 2 + sqrt(5) => 4.23606797749979 Ironically, as somebody new to Ruby, I was just reading about Libraries and Modules so your question was a good review for me. ;) Wayne

on 2011-10-11 13:03

```
On Tue, Oct 11, 2011 at 06:32, Wayne Brissette <waynefb@earthlink.net>
wrote:
> You also have to surround your number in parentheses ().
That's the odd part. Just saying "sqrt 5" works (assuming you've
included Math, else "Math.sqrt 5"). But tack "2 +" on the front, and
suddenly Ruby can't parse it any more, even though it has now *more*
of a clue that what's coming is a mathematical expression.
-Dave
```

on 2011-10-11 13:10

+ is a method that wants one parameter 2 + (Math.sqrt 5) works 2 + Math.sqrt(5) works 2 + Math.sqrt 5 works not

on 2011-10-11 13:15

On Tue, Oct 11, 2011 at 1:02 PM, Dave Aronson <rubytalk2dave@davearonson.com> wrote: > > That's the odd part. Just saying "sqrt 5" works (assuming you've > included Math, else "Math.sqrt 5"). But tack "2 +" on the front, and > suddenly Ruby can't parse it any more, even though it has now *more* > of a clue that what's coming is a mathematical expression. Actually: No. As far as Ruby is concerned, you are chaining method calls (remember: + is a method, not an operator!). That this is a mathematical expression is coincidental A (somewhat) contrived example: "x 2" Is that a method call (x(2)), or do you want to multiply 2 and x? -- Phillip Gawlowski gplus.to/phgaw | twitter.com/phgaw A method of solution is perfect if we can forsee from the start, and even prove, that following that method we shall attain our aim. -- Leibniz

on 2011-10-11 13:52

Phillip Gawlowski wrote in post #1026042: > (remember: + is a method, not an operator!) > > That this is a mathematical expression is coincidental this is a very important point in ruby... `+` is a method (and not an operator, as Phillip pointed out,) that behaves differently with various classes, including but not limited to Integers, Strings, and Arrays - check out the following... irb(main):001:0> p 2 + 5 7 => nil irb(main):002:0> p "two" + "five" "twofive" => nil irb(main):003:0> a1 = ["one", "two", "three"] => ["one", "two", "three"] irb(main):004:0> a2 = [4, 5, 6] => [4, 5, 6] irb(main):005:0> p a1 + a2 ["one", "two", "three", 4, 5, 6] => nil - j

on 2011-10-11 16:17

Yes, I think we all know that; the question is, why does 2 + sqrt(5) parse, but 2 + sqrt 5 does not? I've been wondering this myself - is that syntax somehow ambiguous? 2011/10/11, jake kaiden <jakekaiden@yahoo.com>:

on 2011-10-11 16:33

Don't top post, please. 2011/10/11 Bartosz Dziewoński <matma.rex@gmail.com>: > Yes, I think we all know that; the question is, why does 2 + sqrt(5) > parse, but 2 + sqrt 5 does not? I've been wondering this myself - is > that syntax somehow ambiguous? So, which one shall it be? 2.+.sqrt(5) 2.+(sqrt(5)) 2.+.sqrt.5 2.+(sqrt.5) 2.+(sqrt(5)) -- Phillip Gawlowski gplus.to/phgaw | twitter.com/phgaw A method of solution is perfect if we can forsee from the start, and even prove, that following that method we shall attain our aim. -- Leibniz

on 2011-10-11 16:50

On Tue, Oct 11, 2011 at 4:33 PM, Phillip Gawlowski <cmdjackryan@gmail.com> wrote: > 2.+(sqrt(5)) > 2.+.sqrt.5 > 2.+(sqrt.5) > 2.+(sqrt(5)) I believe the versions which turn a space into a dot are not valid candidates. Or is there any place other than for operators where this happens in Ruby? I mean "a b" can never by "a.b" but must always be "a(b)". That leaves only "2.+(sqrt(5))" on your list (item 2, same as item 5). It's the same with ordinary methods: $ ruby19 -ce '1 + f 2' -e:1: syntax error, unexpected tINTEGER, expecting keyword_do or '{' or '(' $ ruby19 -ce 'a.b c, d e' -e:1: syntax error, unexpected tIDENTIFIER, expecting keyword_do or '{' or '(' $ ruby19 -ce 'a.b c, d(e)' Syntax OK $ ruby19 -ce 'a b, c d' -e:1: syntax error, unexpected tIDENTIFIER, expecting keyword_do or '{' or '(' $ ruby19 -ce 'a b, c(d)' Syntax OK 16:48:16 oz-56838-negative-session-count$ ruby19 -ce 'a.b c, d do end' Syntax OK I think as soon as the comma is missing the end of the argument list or a nested argument list is expected by the parser (which is also indicated by the error message). Kind regards robert

on 2011-10-11 19:53

2011/10/11 Phillip Gawlowski <cmdjackryan@gmail.com>: > Don't top post, please. I was writing from my mobile, it was added automatically (I just don't have an oversized signature to brag about it). No, I do not have the option to disable it. Don't waste everybody's time arguing about top-posting when we're both clearly posting on this list/forum regularly and I clearly do not top post if I can. > 2.+(sqrt.5) > 2.+(sqrt(5)) All but one of these (which you actually repeated twice) are invalid syntax. I think the parser isn't quite *that* stupid, as it clearly understands everything up to "5" (as we can see from the error message), and only then barfs at what a human can understand as an unparentesized argument to method call. Please, try to make more sense when you're being condescending. -- Matma Rex

on 2011-10-11 21:08

On Tue, Oct 11, 2011 at 4:50 PM, Robert Klemme <shortcutter@googlemail.com> wrote: > > I mean "a b" can never by "a.b" but must always be > "a(b)". That leaves only "2.+(sqrt(5))" on your list (item 2, same as > item 5). What about 2.+(2)? It's equivalent to 2 + 2, after all, and not 2(+(2)). "never" is a strong word to use, especially in Ruby. ;) -- Phillip Gawlowski gplus.to/phgaw | twitter.com/phgaw A method of solution is perfect if we can forsee from the start, and even prove, that following that method we shall attain our aim. -- Leibniz

on 2011-10-11 21:15

2011/10/11 Bartosz Dziewoński <matma.rex@gmail.com>: > > All but one of these (which you actually repeated twice) are invalid > syntax. ? That would mean that something like Class.instance_methods(:true).sort wouldn't work. We can chain as many methods as is possible, if we like. P.S.: When I'm condescending, you'll *know* I'm condescending. -- Phillip Gawlowski gplus.to/phgaw | twitter.com/phgaw A method of solution is perfect if we can forsee from the start, and even prove, that following that method we shall attain our aim. -- Leibniz

on 2011-10-11 21:51

On Oct 11, 2011, at 10:17 AM, Bartosz Dziewoński wrote: > Yes, I think we all know that; the question is, why does 2 + sqrt(5) > parse, but 2 + sqrt 5 does not? I've been wondering this myself - is > that syntax somehow ambiguous? Bottom line is that operators have a higher precedence than argument list construction. Let's rewrite the original code with parens showing this: (2 + sqrt) 5 Two adjacent expressions with just white space between them is not valid. Thus the complaint about the unexpected integer. For the original code to be interpreted meaningfully the parser would have to prefer the following precedence: 2 + (sqrt 5) which creates its own problems because now expressions can't easily be used in argument lists: foo 3 + 4, 5 gets parsed as (foo(3) + 4), 5 rather than foo(3 + 4, 5) Bottom line is that operators have a higher precedence than argument list construction. Gary Wright

on 2011-10-11 22:06

On Tue, Oct 11, 2011 at 9:08 PM, Phillip Gawlowski <cmdjackryan@gmail.com> wrote: > On Tue, Oct 11, 2011 at 4:50 PM, Robert Klemme > <shortcutter@googlemail.com> wrote: >> >> I mean "a b" can never by "a.b" but must always be >> "a(b)". That leaves only "2.+(sqrt(5))" on your list (item 2, same as >> item 5). > > What about 2.+(2)? It's equivalent to 2 + 2, after all, and not 2(+(2)). That's a different case because there is an operator between the expressions. My statement only referred to non operator tokens because for operators there always is an equivalent method form. Sorry for not being more explicit about it. > "never" is a strong word to use, especially in Ruby. ;) Even in Ruby syntax there are some hard decisions made. Cheers robert

on 2011-10-11 22:09

On Tue, Oct 11, 2011 at 9:14 PM, Phillip Gawlowski <cmdjackryan@gmail.com> wrote: > 2011/10/11 Bartosz Dziewoński <matma.rex@gmail.com>: >> >> All but one of these (which you actually repeated twice) are invalid >> syntax. > > ? > > That would mean that something like Class.instance_methods(:true).sort > wouldn't work. We can chain as many methods as is possible, if we > like. Yes, but spaces do not become dots except those before an operator. Those forms in your list are not valid transformations of the input. When considering how to group with brackets it only makes sense to consider variants which could be created from the original. Kind regards robert

on 2011-10-12 04:56

On Tue, Oct 11, 2011 at 10:08 PM, Robert Klemme <shortcutter@googlemail.com> wrote: > > Yes, but spaces do not become dots except those before an operator. Except that Ruby doesn't have operators. , -, *, ** are all methods. Granted, they get special treatment, but it's syntactic sugar so that they look like operators. -- Phillip Gawlowski gplus.to/phgaw | twitter.com/phgaw A method of solution is perfect if we can forsee from the start, and even prove, that following that method we shall attain our aim. -- Leibniz

on 2011-10-12 09:55

Phillip Gawlowski wrote in post #1026187: > On Tue, Oct 11, 2011 at 10:08 PM, Robert Klemme > <shortcutter@googlemail.com> wrote: >> >> Yes, but spaces do not become dots except those before an operator. > > Except that Ruby doesn't have operators. , -, *, ** are all methods. > Granted, they get special treatment, but it's syntactic sugar so that > they look like operators. From the point of view of the parser, they are operators. From the point of view of execution, they are method calls. The statement "spaces do not become dots except those before an operator" is not how it works. The expression is parsed just as in any other language: expr / | \ a + b and from this a syntax tree is built equivalent to a.send(:+, b), and then that's what's executed. The reason that a + f b doesn't parse is explained at http://www.ruby-forum.com/topic/2762669#1026142 It's because it parses as (a + f) b. And if the parsing precedence were changed so it became a + (f b), then other undesirable behaviour would result.

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