From: Robert Klemme <shortcutter@...>
Date: 2010-11-02T23:04:38+09:00
Subject: Re: Strange whitespace parsing behavior on Ruby 1.8.7 (patchlevel 249/302)

On Tue, Nov 2, 2010 at 12:19 PM, Colin Bartlett <colinb2r@googlemail.com> wrote:
> On Tue, Nov 2, 2010 at 7:17 AM, Robert Klemme <shortcutter@googlemail.com>wrote:
>
>>
>> Can you repost with proper indentation and line wrapping?
>> Guessing from your text I assume you might have fallen
>> into a unary / binary operator ambiguity.
>>
>
> That seems to be a correct diagnosis. See below for the OP's irb session
> with formatting.
> For the OP:
>
> 7.abs + 3 #=> 10
> 7.abs+3   #=> 10
>
> 7.abs +3   #=> ArgumentError: wrong number of arguments(1 for 0)
> ## Ruby parses the "+" in " +3" as a unary + on 3 giving integer 3,
> ## which means that integer 3 is an argument to abs, hence the error
> message.
>
> def okp( a, b ); a + b; end  #=> nil
>
> okp(4, 7.abs + 3) #=> 14
> okp(4, 7.abs+3)   #=> 14
> okp(4, 7.abs +3)  #=> SyntaxError: (irb):23: syntax error,
>                          #   unexpected tInteger, expecting ")"
> ## I leave that - and the next - one to Robert to explain!
>
> x = '123456'  #=> "123456"
> x.slice(1, x.size -2)  #=> SyntaxError: compile error(irb):63:
>                             # syntax error, unexpected ')',
>                             # expecting kDO_BLOCK
>                             # from (irb):63 from :0
> ## Again, the "-" in " -2" is parsed on a unary on 2 giving integer value
> -2.
> ## Why the ')' is unexpected I leave to Robert!

Very generous. :-)

Concluding from systematic experimentation I believe both errors you
left for me are related to the fact how Ruby parses (or rather: tries
to parse) in absence of brackets:

14:53:27 $ ruby19 -ce 'a(b.c +1)'
Syntax OK
14:53:45 $ ruby19 -ce 'a(d,b.c +1)'
-e:1: syntax error, unexpected tINTEGER, expecting ')'
a(d,b.c +1)
          ^
14:53:50 $ ruby19 -ce 'a(b.c +1,e)'
Syntax OK
14:53:55 $ ruby19 -ce 'a(d,b.c(+1))'
Syntax OK
14:54:08 $ ruby19 -ce 'a((d,b.c)+1)'
-e:1: syntax error, unexpected ')', expecting '='
a((d,b.c)+1)
         ^
-e:1: syntax error, unexpected $end, expecting ')'
14:59:30 $ ruby19 -ce 'a(d,(b.c) +1)'
Syntax OK

It seems that 14:53:45 is parsed like 14:54:08 which is apparently is
illegal because you also cannot do this:

14:54:16 $ ruby19 -ce '(a,b)'
-e:1: syntax error, unexpected '\n', expecting '='

14:58:18 $ ruby19 -ce '(d,b.c +1)'
-e:1: syntax error, unexpected tINTEGER, expecting tCOLON2 or '[' or '.'
(d,b.c +1)
         ^

Hope that sheds some light.

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/