[antlr-interest] v4 "Honey Badger" teaser

[Kyle Ferrio]

Excellent.  I always thought that it should be possible to support
left-recursion with LL(*) but I did not presume that it would be efficient
or easy or wise.  Since I tend to think left-recursively a lot, I am a
happy honey badger, and I parse whatever I want!

Kyle
 On Dec 29, 2011 4:24 PM, "Terence Parr" <parrt at cs.usfca.edu> wrote:

> Hi, For those of you secretly playing with v4 using the repository, don't
> forget that you can use left recursive expression rules now. These are not
> only faster at runtime, they are easier to specify. ANTLR unravels it to
> nonrecursive rules they use semantic predicates to compare operator
> precedence. Here's a sample expression rule for the R language. Believe it
> or not, that crap works in a top-down parser generator. Oh, and there is no
> such thing is parser backtracking a more. The new adaptive LL(*) simply
> makes all the right choices without backtracking in the prediction or in
> the parser.
>
> v4 code name: Honey Badger, after The Crazy Nastyass Honey Badger:
>
> http://www.youtube.com/watch?v=4r7wHMg5Yjg
>
> It's hilarious if you haven't seen it. "ANTLR v4 doesn't care. It's bad
> ass." ;)
>
> Ter
> ------------
> expr    :       '{' exprlist '}'
>        |       '(' expr ')'
>        |       expr '[[' sublist ']' ']'
>        |       expr '[' sublist ']'
>        |       expr ('::'|':::') expr
>        |       expr ('$'|'@') expr
>        |       expr '^'<assoc=right> expr
>        |       ('-'|'+') expr
>        |       expr ':' expr
>        |       expr USER_OP expr
>        |       expr ('*'|'/') expr
>        |       expr ('+'|'-') expr
>        |       expr ('>'|'>='|'<'|'<='|'=='|'!=') expr
>        |       '!' expr
>        |       expr ('&'|'&&') expr
>        |       expr ('|'|'||') expr
>        |       '~' expr
>        |       expr '~' expr
>        |       expr ('->'|'->>'|':=') expr
>        |       expr ('<-'<assoc=right>|'<<-'<assoc=right>) expr
>
>        |       'function' '(' formlist ')' expr
>        |       expr '(' sublist ')'
>
>        |       'if' '(' expr ')' expr
>        |       'if' '(' expr ')' expr 'else' expr
>        |       'for' '(' ID 'in' expr ')' expr
>        |       'while' '(' expr ')' expr
>        |       'repeat' expr
>
>        |       '?' expr
>
>        |       'next'
>        |       'break'
>
>        |       ID
>        |       STRING
>        |       HEX
>        |       INT
>        |       FLOAT
>        |       COMPLEX
>        |       'NULL'
>        |       'NA'
>        |       'Inf'
>        |       'NaN'
>        |       'TRUE'
>        |       'FALSE'
>        ;
>
>
> List: http://www.antlr.org/mailman/listinfo/antlr-interest
> Unsubscribe:
> http://www.antlr.org/mailman/options/antlr-interest/your-email-address
>