Martin Bless's Blog

Railroad diagrams

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Martin Bless
·

5 min read

Right now this is WIP - work in progress!

But let me tell you: Railroad diagrams are a great thing!

Let's start by collecting the pieces

Grammar tools and generators

KGT: Kate's Grammar Tool

Kate's Grammar Tool

Do you want to convert various kinds of BNF to other kinds of BNF? No? Well imagine if you did! This would be the tool for you.

Try it online at arthursonzogni.com/Diagon/#code_area

146.png

Building KGT on Ubuntu 20.04:

git clone https://github.com/katef/kgt.git
cd kgt
sudo apt update
sudo apt install pmake build-essential
pmake
build/bin/kgt --help

Assume this file INPUT.abnf.txt:

expr = term "+" expr / term

term = factor "*" term / factor

factor = "(" expr ")" / const

const = integer

Create all known output formats from file INPUT.abnf.txt:

#!/bin/bash
set -x

# AST - input or output
kgt -l abnf -e abnf     < INPUT.abnf.txt >result.abnf.txt
kgt -l abnf -e bnf      < INPUT.abnf.txt >result.bnf.txt
kgt -l abnf -e iso-ebnf < INPUT.abnf.txt >result.iso-ebnf.txt
kgt -l abnf -e wsn      < INPUT.abnf.txt >result.wsn.txt

# AST - output
kgt -l abnf -e ebnfhtml5 < INPUT.abnf.txt >result.ebnfhtml5.txt
kgt -l abnf -e blab      < INPUT.abnf.txt >result.blab.txt
kgt -l abnf -e dot       < INPUT.abnf.txt >result.dot.txt
kgt -l abnf -e sid       < INPUT.abnf.txt >result.sid.txt

# RRD tree
kgt -l abnf -e rrdot    < INPUT.abnf.txt >result.rrdot.txt
kgt -l abnf -e rrdump   < INPUT.abnf.txt >result.rrdump.txt
kgt -l abnf -e rrll     < INPUT.abnf.txt >result.rrll.txt
kgt -l abnf -e rrparcon < INPUT.abnf.txt >result.rrparcon.txt
kgt -l abnf -e rrta     < INPUT.abnf.txt >result.rrta.txt

# tnode tree
kgt -l abnf -e svg      < INPUT.abnf.txt >result.svg.txt
kgt -l abnf -e rrtext   < INPUT.abnf.txt >result.rrtext.txt
kgt -l abnf -e rrtdump  < INPUT.abnf.txt >result.rrtdump.txt

This is how result.svg.svg looks like: 144.png

Here is result.rrutf8.txt:

expr:
    │├──╮── term ── "+" ── expr ──╭──┤│
        │                         │
        ╰───────── term ──────────╯

term:
    │├──╮── factor ── "*" ── term ──╭──┤│
        │                           │
        ╰───────── factor ──────────╯

factor:
    │├──╮── "(" ── expr ── ")" ──╭──┤│
        │                        │
        ╰──────── const ─────────╯

const:
    │├── integer ──┤│

This is how result.rrtext.txt looks like:

expr:
    ||--v-- term -- "+" -- expr -->--||
        |                         |
        `--------- term ----------'

term:
    ||--v-- factor -- "*" -- term -->--||
        |                           |
        `--------- factor ----------'

factor:
    ||--v-- "(" -- expr -- ")" -->--||
        |                        |
        `-------- const ---------'

const:
    ||-- integer --||

Here is file result.rrta.txt:

add('expr', Diagram(
  Choice(0,
    Sequence(
      NonTerminal("term"),
      Terminal("+"),
      NonTerminal("expr")),
    NonTerminal("term"))));

add('term', Diagram(
  Choice(0,
    Sequence(
      NonTerminal("factor"),
      Terminal("*"),
      NonTerminal("term")),
    NonTerminal("factor"))));

add('factor', Diagram(
  Choice(0,
    Sequence(
      Terminal("("),
      NonTerminal("expr"),
      Terminal(")")),
    NonTerminal("const"))));

add('const', Diagram(
  NonTerminal("integer")));

'tabatkins' generator then can produce output like

grafik.png

tabatkins/railroad-diagrams !!!

Railroad-diagram Generator

A small JS+SVG library for drawing railroad syntax diagrams, like on JSON.org. Now with a Python port!

online demo // Python README

parcon

Parcon is a Python parser combinator library written by Alexander Boyd. It's designed to be easy to learn, easy to use, and to provide informative error messages. Parcon also allows parsing using BNF grammars.

pip install parcon

Sid

sid turns specifications of languages into programs that recognise those languages (Katherine Flavel, The TenDRA Project).

lukaslueg railroad_dsl

A small DSL to generate syntax diagrams

graphics