Categories: parsing



I have been interested in various aspects of parsing since 2009. My research is particularly focused on parsing general context-free grammars, using combinator parsers. I have published several papers, formalized various proofs about parsers in the HOL4 theorem prover, and produced quite a few OCaml implementations to try out various ideas.

Verified parsing

This work produced a verified, sound and complete approach to combinator parsing. This introduced the idea of "good parse trees". The problem with this approach is that it is too inefficient with left-recursive grammars. There is a post describing verified parsing here.


These are projects which I have largely abandoned:

Older links are:

The best documentation for P3 internals is the extended version of the following paper: Tom Ridge. Simple, efficient, sound and complete combinator parsing for all context-free grammars, using an oracle. In Proceedings of SLE 2014. ridge14sle.pdf extended version.

(* _G 1 parses "1", or "1" followed by _G 2; in general, _G n parses
   the number n, optionally followed by _G (n+1); there are an infinite
   number of nonterminals (_G n) generated lazily on demand *)

let _G = ref (fun n -> failwith "")

let _ = _G := fun n -> 
  let an = a (string_of_int n) in
  let alts = lazy(alts[
    (rhs an) >> (fun s -> c s);
    (an >-- (!_G (n+1))) >> (fun (x,y) -> (c x)^y)])
  mkntparser_lazy (mk_pre_parser ()) alts

Related articles:

  • 2018-06-14 A typed DSL for parsing
  • 2018-05-22 First Python program: an Earley parser!
  • 2017-11-14 New OCaml parsing algorithm: tjr_simple_earley
  • 2017-09-17 Two new OCaml libraries: P0 and tjr-csv
  • 2016-02-19 Tree-structured text
  • 2016-02-09 Simple implementation of an Earley-like parsing algorithm
  • 2015-06-26 P5 scala parsing library
  • 2014-12-19 Parsing the IMAP protocol
  • 2014-12-04 Parsing examples
  • 2014-11-21 Talk on parsing at the University of Sussex
  • 2014-09-26 P1 combinator parsing library for OCaml
  • 2014-09-26 E3 earley parser library for OCaml
  • 2014-09-18 SLE 2014 conference, and Parsing at SLE workshop, slides
  • 2014-09-07 ICFP 2014, OCaml workshop, slides and video
  • 2014-07-11 P3 paper accepted for SLE 2014
  • 2014-04-15 New release of P3 code on github
  • 2014-03-02 New release of P3 code on github
  • 2013-12-16 New release of P3 code on github
  • 2013-12-03 Implementing algorithms efficiently
  • 2013-11-08 Talk on parsing and P3 given at Cambridge
  • 2011-12-01 Verified parsing