Re: {Spam?} Re: state in parsers

Yes, the clause is entered when no other rules match.

On 15-12-15 16:23, John Yates wrote:
> Is 'error' a reserved word?  That is can the lexer reliably recognize 
> it and pop context?
>
> On Tue, Dec 15, 2015 at 8:25 AM, Kristof Bastiaensen 
> <[email protected] <mailto:[email protected]>> wrote:
>
>     Hi John,
>
>     I don't disagree, but I didn't design the language.  The parser in
>     ghc has:
>
>         close :: { () }
>                 : vccurly               { () } -- context popped in lexer.
>                 | error                 {% popContext }
>
>
>     popContext is a function that pops the current layout context in
>     the lexer.
>     Would that work in semantic?
>
>     Regards,
>     Kristof
>
>
>     On 14-12-15 18:48, John Yates wrote:
>
>         Kristof,
>
>         [I have not looked at your example, only the text of your most
>         recent question.]
>
>         In the craft of building parsers it is generally considered
>         poor design to have feedback from the parser to the lexer.
>         Ideally the lexer should be able to produce a stream of tokens
>         and quite independently the parser should consume those
>         tokens.  Sometimes the lexer cannot be entirely context free.
>         The quintessential example is parsing declarators in C/C++.
>         See this article for a description:
>
>         https://en.wikipedia.org/wiki/The_lexer_hack
>
>         /john
>
>
>

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