Rule precedence issue with grako

Question

I\'m redoing a minilanguage I originally built on Perl (see Chessa# on github), but I\'m running into a number of issues when I go to apply semantics.

Here is the gr

Answer 1

The problem with your example is that Grako has the nameguard feature enabled by default, and that won't allow parsing just the d when d6 is ahead.

To disable the feature, instantiate your own Buffer and pass it to an instance of the generated parser:

from grako.buffering import Buffer
from myparser import MyParser

# get the text
parser = MyParser()
parser.parse(Buffer(text, nameguard=False), 'expre')

The tip version of Grako in the Bitbucket repository adds a --no-nameguard command-line option to generated parsers.

Answer 2

In Perl, you can use Marpa, a general BNF parser, which supports generalized precedence with associativity (and many more) out of the box, e.g.

:start ::= Script
Script ::= Expression+ separator => comma
comma ~ [,]
Expression ::=
    Number bless => primary
    | '(' Expression ')' bless => paren assoc => group
   || Expression '**' Expression bless => exponentiate assoc => right
   || Expression '*' Expression bless => multiply
    | Expression '/' Expression bless => divide
   || Expression '+' Expression bless => add
    | Expression '-' Expression bless => subtract

Full working example is here. As for programming languages, there is a C parser based on Marpa.

Hope this helps.