Portrait of Daan Leijen

Daan Leijen

Principal Researcher


I am a member of the Research In Software Engineering (RISE) group. I am interested in the design and application of strong type systems, declarative programming, and compiler technology. In particular, I work on algebraic effects and handlers, and working on an implementation as part of the Koka language — a function-oriented language with effect inference.

Some projects that you may be interested in:

  • The Koka language, now with a C backend with excellent performance.
  • The mimalloc allocator: a novel allocator that is a drop-in replacement for `mallloc`/`free` with outstanding performance.
  • The Madoko document system lets you write technical documents and scientific papers in Markdown while generating either Latex or HTML.
  • I wrote the initial task parallel library (TPL) for the .NET parallel extensions, the Haskell standard libraries for Set/Map based on size-balanced trees, and IntSet/IntMap based on bitwise Patricia trees, and the original Parsec parser combinator libraries for Haskell.

I am a permanent member of IFIP working group 2.16 on programming language design, and was chair of the Haskell Symposium steering committee untill 2009. I was on the program committee of
ICFP’19, WPDAI'18 (as part of the WWW'18 conference) in Lyon (Apr 2018), the PADL'18 conference on Practical Aspects of Declarative Languages in LA (Jan 2018, co-located with POPL), the ICFP 2015 conference, the APLAS 2014 conference, the Haskell Symposium 2012, OOPSLA'11, the 2010 ML workshop, the ICFP 2009 conference, and 2004 Haskell workshop. I was the organizer and program chair of the 2013 ML workshop.