EBNF::Grammar Raku package

Introduction

Raku package for Extended Backus-Naur Form (EBNF) parsing and interpretation.

The grammar follows the description of the Wikipedia entry "Extended Backus–Naur form", [Wk1], which refers the proposed ISO/IEC 14977 standard, by R. S. Scowen, page 7, table 1. [RS1, ISO1].

Motivation

The main motivation for this package is to have:

• Multiple EBNF styles parsed

• Grammar generation for multiple languages

I considered extending "Grammar::BNF", but ultimately decided that "Grammar::BNF" needs too much refactoring for my purposes, and, well, it is for BNF not EBNF.

Installation

From Zef ecosystem:

zef install EBNF::Grammar;

From GitHub:

zef install https://github.com/antononcube/Raku-EBNF-Grammar.git

Usage examples

Here is an EBNF grammar for integers and its interpretation into a Raku grammar:

use EBNF::Grammar;

my $ebnf = q:to/END/;
<digit> = '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9' ;
<integer> = <digit> , { <digit> } ;
<TOP> = <integer> ;
END

ebnf-interpret($ebnf);

Here the obtained Raku grammar is evaluated and used to do a few parsings:

my $gr = ebnf-interpret($ebnf):eval;

.say for <212 89 9090>.map({ $gr.parse($_) });

Random sentence generation

Random sentences of grammars given in EBNF can be generated with additional help of the package "Grammar::TokenProcessing", [AAp2].

Here is an EBNF grammar:

my $ebnfCode = q:to/END/;
<statement> = <who> , <verb> , <lang> ;
<who> = 'I' | 'We' ;
<verb> = [ 'really' ] , ( 'love' | 'hate' | { '♥️' } | '🤮' );
<lang> = 'Julia' | 'Perl' | 'Python' | 'R' | 'WL' ;
END

Here is the corresponding Raku grammar:

ebnf-interpret($ebnfCode, name=>'LoveHateProgLang');

Here we generate random sentences:

use Grammar::TokenProcessing;

my $gr = ebnf-interpret($ebnfCode, name=>'LoveHateProgLang'):eval;

.say for random-sentence-generation($gr, '<statement>') xx 12;

CLI

The package provides a Command Line Interface (CLI) script for parsing EBNF. Here is its usage message:

ebnf-parse --help

Implementation notes

1. The first version of "EBNF::Grammar::Standardish" was generated with "FunctionalParsers", [AAp1], using the EBNF grammar (given in EBNF) in [Wk1].

2. Refactored <term> (originally <pTERM>) into separate parenthesized, optional, repeated specs.

   • This corresponds to the design in "FunctionalParsers".

3. Tokens and regexes were renamed. (More concise, easier to read names.)

4. Implemented the "relaxed" version of the standard EBNF.

TODO

• TODO Parsing of EBNF

  • TODO Sequence-pick-left, <&

  • TODO Sequence-pick-right, &>

  • TODO "Named" tokens

    • '_?StringQ' or '_String'

    • '_WordString', '_LetterString', and '_IdentifierString'

    • '_?NumberQ' and '_?NumericQ'

    • '_Integer'

    • 'Range[*from*, *to*]'

• TODO Interpreters of EBNF

  • TODO Java

    • TODO "funcj.parser"

  • TODO Scala

    • TODO built-in

    • TODO parsley

  • MAYBE Python

  • TODO Raku

    • DONE Grammar

    • DONE FunctionalParsers

    • TODO MermaidJS

    • Other EBNF styles

  • TODO WL

    • DONE FunctionalParsers, [AAp1, AAp2]

    • TODO GrammarRules

• DONE CLI

References

Articles

[Wk1] Wikipedia entry, "Extended Backus–Naur form".

[RS1] Roger S. Scowen: Extended BNF — A generic base standard. Software Engineering Standards Symposium 1993.

[ISO1] ISO/IEC 14977:1996.

Packages, repositories

[AAp1] Anton Antonov, FunctionParsers Raku package, (2023), GitHub/antononcube.

[AAp2] Anton Antonov, Grammar::TokenProcessing Raku package, (2022-2023), GitHub/antononcube.