Owen Stephens

Blog🔗

I very occasionally blog about technical things, take a look:

• 20th March 2019: Nickel, an exercise in JIT evaluation
• 25th September 2018: Getting started with the (recent) LLVM C JIT API
• 11th March 2017: gziprb - Gzip implemented in Ruby
• 30th May 2016: Rust MD5
• 6th July 2015: Agda Patience Sort
• 28th September 2014: Determinism costs! A NFA with exponentially bigger DFA
• 24th December 2010: Scala Patience Diff
• 22nd December 2010: C# Pushdown Automaton
• 29th November 2010: Scala implementation of Patience sort
• 19th October 2010: Haskell "Weasel Program" Genetic Algorithm
• 1st October 2010: Linux Kernel Greynet implementation (RFC6018)
• 21st August 2010: foldl implemented using foldr
• 20th August 2010: Haskell composition operator fun: (.).(.)
• 29th October 2009: Why there are only 33 possible IPv4 netmasks

Open Source🔗

A list of open source contributions I’ve made; some are small, but it’s nice to remember them:

• Ruby

  I fixed an N+1 query inside the Rails Postgres adapter for multi-column foreign_keys and unique_constraints.

• Rust

  I traced and fixed the cause of a tabular-layout breaking bug in the CSV toolkit xsv.

• C Ruby

  I extended the Range#cover? method in the MRI Ruby standard library to accept other Range objects to allow easy checking for sub-ranges, as demonstrated in the BigBinary blog that introduces new features coming in Ruby 2.6. Later, I fixed a bug in the Rails implementation of the same feature.

• Ruby

  I diagnosed and fixed a crash-causing bug in the pry Ruby REPL when encountering NULL bytes, which included some MRI source-diving.

• C

  I tracked down and proposed a fix for a segfault in the MRI Ruby interpreter when using forked processes and the default psuedo random number generator, as triggered by the Faker test data library.

• Ruby SQL

  I prevented duplicating of jobs and misleading warnings in the Que-web interface to the Que asynchronous job queue.

• Python

  I fixed a bug to ensure table aliases were correctly taken account of when suggesting completions in the pgcli PostgreSQL CLI tool.

• Ruby

  I added and improved several linters of the popular Rubocop code checking tool:

• Clojure Elixir NodeJS PHP Python Ruby

  I fixed a bug, normalised multi-language implementations and improved test coverage of the Mailchecker project that rejects invalid/throwaway email addresses

• Ruby

  I added support for nested constant definitions to the ripper-tags Ruby ctags generator and later gracefully handled unreadable directories.

• Haskell

  I was a core member of the Darcs VCS team, contributing many patches

• Haskell

  I improved certain error messages of the Cabal packaging tool

• Python

  I added support for IPv6 extension headers to the dpkt library, the google code issue no longer exists, but the changelog (now on GitHub) bears my name

• Haskell

  I added an instance to the Boolean algebra library Cond to recognise that Boolean algebras are closed under pairing

Research🔗

My research took place as part of a Masters and PhD in Computer Scence. The two main topics I studied were model checking of Petri Nets (specifically, compositional reachability checking) and functional programming languages (specifically, methods of implementing IO).

Compositional model checking of Petri Nets🔗

My PhD research focussed on compositionally checking reachability in systems modeled by Petri nets. My PhD thesis Compositional specification and reachability checking of net systems is available online, and includes the work from three papers I co-authored:

• Compositional Reachability in Petri Nets, Reachability Problems ‘14 with Julian Rathke and Paweł Sobociński, paper (PDF)
• A Programming Language for Spatial Distribution of Net Systems, Petri Nets ‘14 with Paweł Sobociński, paper (PDF)
• Penrose: Putting Compositionality to Work for Petri Net Reachability, CALCO’13 with Paweł Sobociński, paper (PDF)

IO in functional programming languages🔗

My Masters research project investigated methods of implementing input/output (I/O) in functional programming languages: report (PDF).