Feature request: add language from the "Railroad-diagram Generator"

[dolmen]

Add support for the language from the Railroad-diagram Generator as input.

Example:

Diagram(
  Optional('+', 'skip'),
  Choice(0,
    NonTerminal('name-start char'),
    NonTerminal('escape')),
  ZeroOrMore(
    Choice(0,
      NonTerminal('name char'),
      NonTerminal('escape'))))

Online:
https://tabatkins.github.io/railroad-diagrams/generator.html

Format documentation:
https://github.com/tabatkins/railroad-diagrams#components

[katef]

Hi! Thanks! This is interesting. kgt's input is usually BNF, which is supposed to be a semantic representation of a grammar. Tab's structure here is for presentational information. For example, it offers Stack() for vertically placed alts.

kgt has several stages internally. Relevant here are the AST for BNF, and then the RRD tree (which is presentational, although still abstracted from layout coordinates).

So we'd have two options for parsing this;

• to disregard the presentational parts, and construct the BNF AST as if it were any other BNF input.
• to construct the RRD node tree directly. although it doesn't currently offer a Stack() construct, so we'd still skip that.

Both could make sense.

https://github.com/katef/kgt/blob/main/src/ast.h
https://github.com/katef/kgt/blob/main/src/rrd/node.h