A Fast and Loose LBNF to SDF3 Converter

In response to popular demand I have created a Spoofax project for LBNF, the grammar formalism of the BNFC project. The project contains an SDF3 definition for LBNF obtained by manually converting the LBNF grammar in LBNF, and a transformation from LBNF to SDF3.

The transformation is fairly straightforward since LBNF and SDF3 productions are similar. In particular, LBNF productions declare a constructor symbol, which is also needed in SDF3. The main distinction is the way that lists are specified. For example, the following LBNF productions

Rule . Def ::= Label "." Cat "::=" [Item] ;
[]  . [Item] ::= ;
(:) . [Item] ::= Item [Item] ;

translate to this SDF3 production:

Def.Rule = [[Label] . [Cat] ::= [{Item " "}*]]

The transformation is probably somewhat rudimentary and ignores advanced features of LBNF. Yet the converter should be fairly robust, since it skips anything that it doesn’t recognize. I have only tested it on the LBNF.cf file itself. More testing is needed. I will be happy to do some more work on the transformation if popular demand so requires.

Using LBNF to SDF3

To use the converter:

Check out the GitHub repository (https://github.com/MetaBorgCube/metaborg-lbnf) and import the project into your Eclipse with Spoofax.
Build the project.
Open a .cf file
Hit the ‘Transform to SDF3’ transformation in the ‘Generation’ menu

LBNF in LBNF (fragment)

MkGrammar . Grammar ::= [Def] ;

[]  . [Def] ::= ;
(:) . [Def] ::= Def ";" [Def] ;

[]  . [Item] ::= ;
(:) . [Item] ::= Item [Item] ;

Rule . Def ::= Label "." Cat "::=" [Item] ;

Terminal  . Item ::= String ;
NTerminal . Item ::= Cat ;

ListCat  . Cat ::= "[" Cat "]" ;

LBNF in SDF3 (same fragment)

context-free syntax
  Grammar.MkGrammar = {Def ";"}*

  Def.Rule = [[Label] . [Cat] ::= [{Item " "}*]]

  Item.Terminal = STRING

  Item.NTerminal = Cat

  Cat.ListCat = <[ <Cat> ]>

Using LBNF to SDF3
LBNF in LBNF (fragment)
LBNF in SDF3 (same fragment)