Breaking associativity in OMeta

grammar.ometajs

var ometajs = require('ometajs'),
    Parser = ometajs.grammars.BSJSParser;

// Source: http://tratt.net/laurie/research/pubs/html/tratt__direct_left_recursive_parsing_expression_grammars/

// '1-2-3' -> ((1-2)-3)
ometa a <: Parser {
    Expr = Expr:l "-" Num:r -> [l, '-', r]
        | Num:i -> [i],
    Num = /[0-9]+/
}

// '1-2-3' -> (1-(2-3))
ometa arr <: Parser {
    Expr = Expr:l "-" Expr:r -> [l, '-', r]
        | Num:i -> [i],
    Num = /[0-9]+/
}

test.js

var ometajs = require('ometajs'),
    grammars = require('./grammar');

// Adding right-recursive invocation to a left-recurive rule changes
// parsing associativity


grammars.a.matchAll('1-2-3', 'Expr');
grammars.arr.matchAll('1-2-3', 'Expr');


grammars.b.matchAll('1+2-3', 'Expr');
grammars.brr.matchAll('1+2-3', 'Expr');