From: dblack@...
Date: 2006-02-12T21:47:24+09:00
Subject: Re: Parse error within Regexp

Hi --

On Sun, 12 Feb 2006, Mauricio Fernandez wrote:

> On Sun, Feb 12, 2006 at 11:42:42AM +0900, dblack@wobblini.net wrote:
>>> Would something like this make sense?
>>>
>>> $  ./ruby19 -e '"".scan / ,/'
>>> -e:1: syntax error, unexpected ','
>>> "".scan / ,/
>>>          ^
>>> -e:1: unterminated regexp meets end of file
>>>                 ========
>>
>> I'm not sure the "unterminated string" makes sense as the error
>> message, but I don't think it's an unterminated regex either.  It
>> seems that Ruby sees the first / as division, so it doesn't consider
>> itself to be in mid-regex.  If it thought it was in mid-regex, it
>> would presumably keep going and it would find that the regex *is*
>> terminated.
>
> I think the second '/' marks the start of the regexp, as seen by
> the parser in that case (erroneously of course, but read below):
>
> "".scan / ,/   <----------------------------
>          ^                                  \
> this is the unexpected ,                  and this the unterminated regexp
>
> Compare that to
>
> $ ruby -e '"".scan / , " '
> -e:1: syntax error, unexpected ','
> "".scan / , "
>           ^
> -e:1: unterminated string meets end of file
> -e:1: warning: useless use of a literal in void context
>
> The parser is doing its best to keep parsing so it can report further
> errors.

Perhaps, but I don't think "unterminated regexp" describes the
situation very well.  Of course the real situation is: I'm getting a
barrage of strange error messages so something must be *really* wrong
:-)

> Besides, consider this case:
>
> $ ruby19 -e 'puts ARGF.read.scan /[-+]?(\d+(?:\.\d+)?)(?=[^\d])'
> -e:1: warning: ambiguous first argument; put parentheses or even spaces
> -e:1: unterminated string meets end of file
> -e:1: syntax error, unexpected tSTRING_END, expecting tSTRING_CONTENT or tREGEXP_END or tSTRING_DBEG or tSTRING_DVAR
>
> I think the following makes more sense and is less noisy too:
>
> ~/src/ruby/ruby.head$ ./ruby19 -e 'puts ARGF.read.scan /[-+]?(\d+(?:\.\d+)?)(?=[^\d])'
> -e:1: warning: ambiguous first argument; put parentheses or even spaces
> -e:1: unterminated regexp meets end of file
> -e:1: warning: parenthesize argument(s) for future version

That's a different case, though: that's truly an unterminated regexp.


David

-- 
David A. Black (dblack@wobblini.net)
Ruby Power and Light (http://www.rubypowerandlight.com)

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