Joachim Breitner

Teaching to read Haskell

Published 2019-01-11 in sections English, Haskell.

TL;DR: New Haskell tutorial at

Half a year ago, I left the normal academic career path and joined the DFINITY Foundation, a non-profit start-up that builds a blockchain-based “Internet Computer” which will, if everything goes well, provide a general purpose, publicly owned, trustworthy service hosting platform.

DFINITY heavily bets on Haskell as a programming language to quickly develop robust and correct programs (and it was my Haskell experience that opened this door for me). DFINITY also builds heavily on innovative cryptography and cryptographic protocols to make the Internet Computer work, and has assembled an impressive group of crypto researchers.

Crypto is hard, and so is implementing crypto. How do we know that the Haskell code correctly implements what the cryptography researchers designed? Clearly, our researchers will want to review the code and make sure that everything is as intended.

But surprisingly, not everybody is Haskell-literate. This is where I come in, given that I have taught Haskell classes before, and introduce Haskell to those who do not know it well enough yet.

At first I thought I’d just re-use the material I created for the CIS 194 Haskell course at the University of Pennsylvania. But I noticed that I am facing quite a different audience. Instead of young students with fairly little computer scientist background who can spent quite a bit of time to learn to write Haskell, I am now addressing senior and very smart computer scientists with many other important things to do, who want to learn to read Haskell.

Certainly, a number of basics are needed in either case; basic functional programming for example. But soon, the needs diverge:

  • In order to write Haskell, I have to learn how to structure a program, how to read error message and deal with Haskell’s layout rule, but I don’t need to know all idioms and syntax features yet.
  • If I want to read Haskell, I need to navigate possibly big files, recognize existing structure, and deal with a plenitude of syntax, but I don’t need to worry about setting up a compiler or picking the right library.

So I set out to create a new Haskell course, “Haskell for Readers”, that is specifically tailored to this audience. It leaves out a few things that are not necessary for reading Haskell, is relatively concise and densely packed, but it starts with the basics and does not assume prior exposure to functional programming.

As it behooves for a non-profit-foundation, DFINITY is happy for me to develop the lecture material in the open, and release it to the public under a permissive creative commons license, so I invite you to read the in-progress document, and maybe learn something. Of course, my hope is to also get constructive feedback in return, and hence profit from this public release. Sources on GitHub.


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