In the Theory Lunch of the last week, James Chapman talked about the MU puzzle from Douglas Hofstadter’s book *Gödel, Escher, Bach*. This puzzle is about a string rewriting system. James presented a Haskell program that computes derivations of strings. Inspired by this, I wrote my own implementation, with the goal of improving efficiency. This blog post presents this implementation. As usual, it is available as a literate Haskell file, which you can load into GHCi. Continue reading

# Author Archives: Wolfgang Jeltsch

# The Constraint kind

A recent language extension of the Glasgow Haskell Compiler (GHC) is the `Constraint`

kind. In this blog post, I will show some examples of how this new feature can be used. This is a write-up of my Theory Lunch talk from 7 February 2013. The source of this article is a literate Haskell file, which you can download and load into GHCi. Continue reading

# Some interesting features of Haskell’s type system

One of the most important ingredients of Haskell is its type system. Standard Haskell already provides a lot of useful mechanisms for having things checked at compile time, and the language extensions provided by the Glasgow Haskell Compiler (GHC) improve heavily on this.

In this article, I will present several of Haskell’s type system features. Some of them belong to the standard, others are only available as extensions. This is a write-up of a talk I gave on 31 January 2013 during the Theory Lunch of the Institute of Cybernetics. This talk provided the basics for another Theory Lunch talk, which was about the `Constraint`

kind. Continue reading

# Three talks about ideal monads

Two months ago, we started the theory lunch meetings at the Institute of Cybernetics. In these meetings, we have lunch together and discuss all kinds of interesting things related to theoretical computer science. We also started the Theory Lunch blog, where an article is posted for every lunch session. I used three of the lunch meetings to talk about ideal monads, and published summaries of my talks in the following articles: Continue reading

# New paper about a generalization of FRP and causality in categorical models

Yesterday I finished my new paper *Temporal Logic with “Until”, Functional Reactive Programming with Processes, and Concrete Process Categories*, which will appear in the proceedings of PLPV ’13 and is also available online. I have already given two talks on topics of this paper, one at the Joint Estonian–Latvian Theory Days at Medzābaki and another one at the Theory Seminar of the Institute of Cybernetics. Continue reading

# Paper on categorical models of temporal logic and FRP published

My MFPS ’12 paper *Towards a Common Categorical Semantics for Linear-Time Temporal Logic and Functional Reactive Programming* has just been officially published by Elsevier. Continue reading

# ucs 2.1 soon to appear on CTAN

I have just uploaded version 2.1 of the LaTeX ucs package to CTAN, so it should appear there within the next few days. Some small bugs have been fixed, and mappings for several characters, mostly musical notes and special arrows, have been added. A big thank you goes to Ralf Meyer, who has contributed considerably to this release. Continue reading