Left Recursion in Pest Grammar Parsing Tool

help
1

Hi All,

I am tyring to do SQL parsing using Pest Grammar Files.

I converted the below Teradata Antlr grammar file to rust and I get the left recursive error

section [204 to 229 ] of ANTLR code. from the above file having issue.

expr
: literal_value
| column_name
| unary_operator expr
| expr '||' expr
| expr ( '' | '/' | '%' ) expr
| expr ( '+' | '-' ) expr
| expr ( '<' | '<=' | '>' | '>=' ) expr
| expr ( '=' | '==' | '!=' | '<>' | K_IS | K_IS K_NOT | K_IN | K_LIKE ) expr
| expr K_AND expr
| expr K_OR expr
| function_name '(' ( K_DISTINCT? expr ( ',' expr ) | '' )? ')'
| '(' expr ')'
| K_CAST '(' expr K_AS type_name ')'
| expr K_NOT? K_LIKE expr ( K_ESCAPE expr )?
| expr ( K_IS K_NULL | K_IS K_NOT K_NULL | K_NOT K_NULL )
| expr K_IS K_NOT? expr
| expr K_NOT? K_BETWEEN expr K_AND expr
| expr K_NOT? K_IN ( OPEN_PAR ( select_expr
| expr ( ',' expr )
)?
CLOSE_PAR
| ( database_name '.' )? table_name )
/*| ( ( K_NOT )? K_EXISTS )? '(' select_stmt ')' */
| K_CASE expr? ( K_WHEN expr K_THEN expr )+ ( K_ELSE expr )? K_END
;

I think above scenario is similar to below code.

expr1 = {ASCII_DIGIT
|expr1~("+"|"-")~expr1
}

If I try to parse the statement 2+2+3 then grammar parser only 2 and not the rest. So how can we resolve this.

I am newbie to grammar parsing. Thanks for your help in advance.

Thanks,
Vignesh

2

According to crates.io, Pest is based on PEG technology.
Parsing Expression Grammars, much like LL(*) parsers, can't perform left recursion because it can and will lead to infinite recursion.
Your choices are either rewriting your grammar to not need left recursion at all, or moving on from Pest to a different parser generator.