Hai (Paul) Liu

As great scientists have said and as all children
know, it is above all by the imagination that
we achieve perception, and compassion, and hope.


I'm interested in functional programming and programming language research in general. I did my PhD with Professor Paul Hudak at Yale University. I was part of the Yale Haskell Group. After being a research scientist at Intel Labs for 7 years, I am now at DFINITY. I can be reached at hai dot liu at aya dot yale dot edu.


PC member of Haskell Symposium 2015.
PC member of 26th Symposium on Implementation and Application of Functional Languages (IFL'14).
PC member of The 3rd ACM SIGPLAN Workshop on Functional High-Performance Computing (FHPC'14).
PC member of the Haskell Implementors Workshop 2014 (HIW'14).


Todd A. Anderson, Hai Liu, Lindsey Kuper, Ehsan Totoni, Jan Vitek, Tatiana Shpeisman. Parallelizing Julia with a Non-invasive DSL. Proceedings of the 2017 European Conference on Object-Oriented Programming (ECOOP'17). Barcelona, Spain. June 21-23, 2017. [ abstract | bibtex | pdf | slides ]

Jeremy Yallop, Hai Liu. Causal Commutative Arrows Revisited. Proceedings of the 2016 ACM SIGPLAN symposium on Haskell, Nara, Japan, September 22–23, 2016. [ abstract | bibtex | pdf | slides ]

Leonard Truong, Rajkishore Barik, Ehsan Totoni, Hai Liu, Chick Markley, Armando Fox, and Tatiana Shpeisman. Latte: a language, compiler, and runtime for elegant and efficient deep neural networks. In Proceedings of the 37th ACM SIGPLAN Conference on Programming Language Design and Implementation, pp. 209-223. ACM, 2016. [ abstract | bibtex | pdf ]

Hai Liu, Laurence E. Day, Neal Glew, Todd A. Anderson, and Rajkishore Barik. Native Offload of Haskell Repa Programs to Integrated GPUs. The 3rd ACM SIGPLAN Workshop on Functional High-Performance Computing. FHPC'14, Gothenburg, Sweden. September 04, 2014. [ abstract | bibtex | pdf | slides ]

Leaf Petersen, Todd A. Anderson, Hai Liu, and Neal Glew. Measuring The Haskell Gap. Post Symposium Submission to The 25th International Symposium on Implementation and Application of Functional Languages. Radboud University Nijmegen, The Netherlands. August 28-30, 2013. (Winner of Peter Landin prize) [ abstract | bibtex | pdf ]

Hai Liu, Neal Glew, Leaf Petersen, and Todd A. Anderson. The Intel Labs Haskell Research Compiler. Proceedings of the 2013 ACM SIGPLAN symposium on Haskell, Boston, MA, USA. September 23-24, 2013. [ abstract | bibtex | pdf | slides ]

Daniel Winograd-Cort, Hai Liu, and Paul Hudak. Virtualizing Real-World Objects in FRP. Practical Aspects of Declarative Languages - 14th International Symposium, PADL 2012, Philadelphia, PA, USA, January 23-24, 2012. [ abstract | bibtex | pdf ]

Hai Liu, Eric Cheng, and Paul Hudak. Causal Commutative Arrows. Journal of Functional Programming, volume 21, issue 4-5, pp. 467-496. September 2011. (Extended journal version of our ICFP09 paper.) [ abstract | bibtex | pdf ]

Hai Liu. The Theory and Practice of Causal Commutative Arrows. Ph.D. Thesis. Computer Science Department, Yale University. May 2011. [ abstract | bibtex | pdf | slides ]

Zhijing G. Mou, Hai Liu, and Paul Hudak. Compress-and-Conquer for Optimal Multicore Computing. The Fifth Workshop on Declarative Aspects of Multicore Programming (DAMP2010), Madrid, Spain. January 2010. [ abstract | bibtex | pdf ]

Hai Liu, and Paul Hudak. An Ode to Arrows. Twelfth International Symposium on Practical Aspects of Declarative Languages - PADL'10. Madrid, Spain. January 2010. [ abstract | bibtex | pdf ]

Hai Liu, Eric Cheng, and Paul Hudak. Causal Commutative Arrows and Their Optimization. Proceedings of the 14th ACM SIGPLAN International Conference on Functional Programming (ICFP 2009). Edinburgh, Scotland. August 2009.   [ abstract | bibtex | pdf | slides ]

Hai Liu, and Paul Hudak. Plugging a Space Leak with an Arrow. Electronic Notes in Theoretical Computer Science. 193 (Nov. 2007), 29-45.   [ abstract | bibtex | pdf ]

Hao Wang, Yang Richard Yang, Paul H. Liu, Jia Wang, Alex Gerber, and Albert Greenberg. Reliability as an Interdomain Service. In Proceedings of ACM SIGCOMM, Kyoto, Japan, August 2007. [ abstract | bibtex | pdf ]

K.Y. Leong, H. Liu, O.P. Wu. Unicode, Java and Input Methods, Twelfth International Unicode Conference, Tokyo, Japan. (Apr 1998)


Here are some software projects that I've worked on. They may be school or work related, or just of personal interest. Only open source projects are listed here although some are yet to be made public. The list of commercial ones can be found in my resume.

Parallel Accelerator for Julia and for Python aimed to bring performance to scripting languages on parllel hardware with a non-invasive DSL (Domain Specific Language) approach, with the hope to benefit numeric computing and data science communities in general, where such languages are popular among scientists without formal CS background.

Functional Language Research Compiler (FLRC) was designed to be a general compiler framework for functional languages. The only supported compiler that is being released is a Haskell Research Compiler (HRC). At the core of FLRC is a craftly designed intermediate representation (IR) called MIL that marries high-level object representation to low-level control flow. It was also a research vehicle we used to study the performance of functional languages on modern parallel hardware architectures.

Site Tool is a minimalistic approach to personal document and web page writing, or to put it simply, pandoc + make + darcs. It is sort of like a personal Wiki, but without involving any web server, or the clunky edit box in a browser. It is an early effort towards my ideal of the web-age human computer interface: a digital notebook where one continuously writes, reads, and cross-links, and on top of which, one shares such efforts with others.


CCA is a pre-processor and optimizer for Causal Commutative Arrows, which is a more constrained class of Arrows with two additional laws: commutativity and product. It implements the normalization algorithm presented in our paper using Template Haskell to provide staged compilation of generic CCA arrows, with speedups sometimes over two orders of magnitude. The pre-processor is based on Paterson's arrowp preprocessor but specialized to deal with CCA. Latest development version can be found in its darcs repository.


Euterpea is a new Haskell library for computer music applications developed at the Yale Haskell Group. It is a descendent of Haskore and HasSound, and is intended for both educational purposes as well as serious computer music development. Euterpea is a wide-spectrum library, suitable for high-level music representation, algorithmic composition, and analysis; mid-level concepts such as MIDI; and low-level audio processing, sound synthesis, and instrument design. The name Euterpea is derived from Euterpe, who was one of the nine Greek Muses (goddesses of the arts), specifically the Muse of Music. My contribution include the real-time MIDI I/O, as well as a Musical User Interface that enables a set of computer-music specific GUI widgets such as keyboards, guitar frets, knobs, sliders, and so on. Yale ITS had an article about our work behind this. The software is under active development and can be obtained from its darcs repository.


HWiki is a custom Wiki engine written in Haskell to provide online book editing and sharing, and PDF publication to e-ink reader devices including iRex iLiad, Sony Reader, Amazon Kindle DX and a few others. It runs as a SCGI program, serves an AJAX interface (borrowed from Orchid), and relies on Pandoc to parse Markdown syntax. Notable features include automatic segmentation of big files into smaller chunks, and a built-in special purpose revision control system that supports millons of small files because neither git or darcs is up to the task. The software has also been licensed (in GPL) by some commercial user.


LambdaINet is an experimental Interaction Net evaluator written in Haskell that implements optimal evaluation for Lambda calculus based on Lambdascope. It features an interactive graphical user interface that helps understanding optimal as well as other reduction strategies. Not included at the moment is a prototypical implementation of a fine-grain parallel reduction system (complete with a concurrent garbage collector) for Interaction Nets that is both lock-free and wait-free. Few implementations exist for optimal evaluation, I'm proud that this is one of them.


GLFW is a is a Haskell module for GLFW OpenGL framework. It provides an alternative to GLUT for OpenGL based Haskell programs. I initially started this project as an effort to port SOE software to a modern cross-platform graphics interface. The latest version is a cabal install away from Hackage DB, and its development is now coordinated through the mailinglist and darcs repsitory.

The following are past projects no longer being maintained. Source codes are distributed as they are, and I have no knowledge whether they still compile or work at all.


AwkiAwki is a WikiWiki clone written in awk by Oliver Tonnhofer. I've made numerous extensions to the original to support attachments, code inlining, header index, user authentication, comment posting, etc. etc. The latest version of my branch is made available in source. I've stopped developing it further since I moved on to the Haskell based HWiki.


Incremental Garbage Collector is a patch for Lua 4.0 that implements a tri-color algorithm so as to reduce apparent GC pause during Lua script execution, and to meet critical requirements for applications like games. The patch was written and released in 2002, and obsoleted by Lua 5.1 when the latter came out in 2005 with a built-in incremental collector.


GEEP is a multi-channel communication protocol to replace TCP, or put in another way, a reliable data transport layer on top of UDP, developed at GIME International in 2001. It features minimal connection maintenance overhead, built-in multi-channel control within same connection, selective acknowledgement to reduce network load, and enhanced Vegas transmission control mechanisms to speed up transfer by fully utilizing available bandwidth. GEEP has served well as data protocol between game client and server, as well as in a generic software auto-update service.


GIME is a generic engine that supports multi-threading, internationalization, database, multiple interfaces including web, telnet and graphic clients on which massive multi-user interactive applications could be built with little effort. It was the first open technology developed at GIME International back in 2001. Its SourceForge repository provides the backend server (written in Pike), frontend GUI tools (written in Lua and C), and a demo groupware built with GIME (also with Roxen webserver). There was also a later unreleased version written in Haskell which served a WAP game for cellphones, but that was more of an experiment than a real product.


SGZ MUD is a text-based Chinese MUD (Multi-User Dungeon) with a background set in the Three Kingdoms era. It started in 1998 after I localized a version of Lima Mudlib in Chinese, and soon became a rare gem among popular Chinese MUDs at the time due to its unique strategy play. The enthusiasm about the game led us to start a company to develop it further to eventually become the GIME engine and the Century of Three Kingdoms MMOG. SGZ mudlib (excluding player data) is made available as LPC source codes, and you need a version of MudOS driver (or precompiled i386 Linux binary) to run it.