Encoding monadic computations in C# using iterators

Tomas Petricek

In Proceedings of ITAT 2009

Many programming problems can be easily solved if we express them as computations with some non-standard aspect. This is a very important problem, because today we are struggling to efficiently program multi-core processors and to write asynchronous code. Unfortunately main-stream languages such as C# do not support any direct way for encoding unrestricted non-standard computations. In languages like Haskell and F#, this can be done using monads with syntactic extensions they provide and it has been successfully applied to a wide range of real-world problems.

In this paper, we present a general way for encoding monadic computations in the C# 2.0 language with a convenient syntax using a specific language feature called iterators. This gives us a way to use well-known non-standard computations enabling easy asynchronous programming or for example the use of software transactional memory in plain C#. Moreover, it also opens monads in general to a wider audience which can help in the search for other useful and previously unknown kinds of computations.

Paper and more information

• Download the paper (PDF) and supplementary materials (PDF)
• Look at the C# source code (ZIP)
• For more information read a related blog post
• View the slides from ITAT talk (PDF)

Corrections

This paper contains a number of issues. Most importantly, it ignores the fact that C# 2.0 iterators keep mutable state, which makes running a continuation multiple times harder (as a result, it is only possible to easily encode one-shot continuations).

This limits the applicability of this approach. However, the paper is still interesting, especially since many main-stream languages (including Python and JavaScript) are attempting (as of 2013) to apply the approaches discussed in the paper.

Bibtex

If you want to cite the paper, you can use the following BibTeX information, or get full details from the paper proceedings in CEUR-WS.

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@inproceedings{iterators-itat09,
  author    = {Petricek, Tomas},
  title     = {Encoding monadic computations in C\# using iterators},
  booktitle = {Proceedings of the Conference on Theory and
               Practice of Information Technologies},
  series    = {ITAT 2009},
  location  = {Kralova studna, Slovakia},
  year      = {2009}
}

If you have any comments, suggestions or related ideas, I'll be happy to hear from you! Send me an email at tomas@tomasp.net or get in touch via Twitter at @tomaspetricek.