[antlr-interest] Looping forever on some input

[Thomas Brandon]

The problem is most likely your DecimalLiteral rule:
DecimalLiteral
    :
    ;
Non-fragment lexer rules that can match no input will cause infinite loops.
This may only occur for certain input as other input will be matched
before ANTLR checks whether the troublesome rule can match. Having
input that matches no other rule ensures such a rule will cause an
infinite loop.

Tom.

On Thu, Apr 2, 2009 at 7:09 PM, Ola Bini <ola.bini at gmail.com> wrote:
> Hi,
>
> I'm having some trouble with the lexer looping forever on input that
> should be possible to disambiguate in limited time. Not exactly sure why
> this happens. It is definitely possible I have done something stupid in
> my grammar, of course.
>
> I've seen eternal looping before, for some constructs. A typical example
> was the input of a single quote, before defining anything that allows a
> single quote. This behavior seems a bit strange, in my opinion, but I
> never figured out why it happened.
>
> The current problem is for input such as "::foo". (without the double
> quotes).
>
> The relevant productions (the only ones that include colon) look like this:
> fragment
> OperatorChar
>    :
>       '+'  | '-' | '*' | '%' | '<'
>    |  '>'  | '!' | '?' | '~' | '&'
>    |  '|'  | '^' | '$' | '=' | '@'
>    |  '\'' | '`' | ':'
>    ;
>
> Identifier
>    :
>        '[]'
>    |   '{}'
>    |   (OperatorChar | '/') (OperatorChar | '#' | '/')*
>    |   '#' (OperatorChar | '#')+
>    |   '.' '.'+
>    |   Letter (Letter|IDDigit|':'|'!'|'?'|'$')*
>    |   ':' (Letter|IDDigit) (Letter|IDDigit|':'|'!'|'?'|'$')*
>    ;
>
> Where Identifier is part of the main production for the parser.
>
> The full grammar can be seen at:
> http://github.com/olabini/ioke/raw/9e2795c9c5f2b326c0cbb3dfb456f885b9625ba2/src/grammar/ioke.g
>
>
> Cheers
>
> --
>  Ola Bini (http://olabini.com)
>  Ioke creator (http://ioke.org)
>  JRuby Core Developer (http://jruby.org)
>  Developer, ThoughtWorks Studios (http://studios.thoughtworks.com)
>  Practical JRuby on Rails (http://apress.com/book/view/9781590598818)
>
>  "Yields falsehood when quined" yields falsehood when quined.
>
>
>
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