Winter is coming even more quickly – Blog – Joachim Breitner's Homepage
TL;DR: I explain how I improved the performance of an interpreter for WebAssembly written in Haskell by plucking some low-hanging fruit. Background Motivated by my work at the DFINITY Foundation, I was looking into interpreters for WebAssembly written in Haskell, and found my colleague John Wiegley’s winter: A straight-forward port of the WebAssembly reference interpreter, written in Ocaml by Andr
The magic “Just do it” type class – Blog – Joachim Breitner's Homepage
One of the great strengths of strongly typed functional programming is that it allows type driven development. When I have some non-trivial function to write, I first write its type signature, and then the writing the implementation often very obvious. Once more, I am feeling silly In fact, it often is completely mechanical. Consider the following function: foo :: (r -> Either e a) -> (a -> (r ->
Finding bugs in Haskell code by proving it – Blog – Joachim Breitner's Homepage
Last week, I wrote a small nifty tool called bisect-binary, which semi-automates answering the question “To what extent can I fill this file up with zeroes and still have it working”. I wrote it it in Haskell, and part of the Haskell code, in the Intervals.hs module, is a data structure for “subsets of a file” represented as a sorted list of intervals: data Interval = I { from :: Offset, to :: Off
veggies: Haskell code generation from scratch – Blog – Joachim Breitner's Homepage
How hard it is to write a compiler for Haskell Core? Not too hard, actually! I wish we had a formally verified compiler for Haskell, or at least for GHC’s intermediate language Core. Now formalizing that part of GHC itself seems to be far out of reach, with the many phases the code goes through (Core to STG to CMM to Assembly or LLVM) and optimizations happening at all of these phases and the many
Showcasing Applicative – Blog – Joachim Breitner's Homepage
My plan for this week’s lecture of the CIS 194 Haskell course at the University of Pennsylvania is to dwell a bit on the concept of Functor, Applicative and Monad, and to highlight the value of the Applicative abstraction. I quite like the example that I came up with, so I want to share it here. In the interest of long-term archival and stand-alone presentation, I include all the material in this
The Incredible Proof Machine – Blog – Joachim Breitner's Homepage
In a few weeks, I will have the opportunity to offer a weekend workshop to selected and motivated high school students1 to a topic of my choice. My idea is to tell them something about logic, proofs, and the joy of searching and finding proofs, and the gratification of irrevocable truths. While proving things on paper is already quite nice, it is much more fun to use an interactive theorem prover,
ZuriHac 2015 – Blog – Joachim Breitner's Homepage
Last weekend, I attended ZuriHac 2015, which was, as always, a pleasant event. I did not actually do a lot, besides some maintenance of Debian Haskell packages, but had some nice chats. It is always very motivating to hear that people read my blog, or that they found my talk (such as the Haskell Bytes talk at Galois) helpful. My plan was to work on gipeda and perf.haskell.org. I did not do much un
ZuriHac 2014 – Blog – Joachim Breitner's Homepage
I’m writing this on the train back from the ZuriHac Haskell Hackathon in Zürich, generously sponsored by Better and Google. My goal for this event was to attract new people to work on GHC, the Haskell compiler, so I announced a „GHC bugsquashing project“. I collected a few seemingly simple ticket that have a good effort/reward ratio for beginners and encouraged those who showed up to pick one to w
Adding safe coercions to Haskell – Blog – Joachim Breitner's Homepage
Yesterday, I pushed my first sizable contribution to GHC, the Haskell compiler. The feature solves the problem that newtypes are not always free: If we have newtype Age = MkAge Int, then we have all learned that the Age function has zero run-time cost. But if the Int that we want to convert is inside another type, the conversion is no longer free: Converting a Maybe Int to a Maybe Age using, for e
Constructing a list in a Monad – Blog – Joachim Breitner's Homepage
In Haskell, lists are ubiquitous. In real-world Haskell, monads are ubiquitous. So it should be an easy task to fill a list with values obtained in a monad, i.e. a list of n random numbers (in the Rand monad), or getting some input from the user, and storing it in a list, until the user chooses to finish the input. The task For now, assume a function getInput :: IO Int; we want to run it 10000 and
Real World Haskell Applications – Blog – Joachim Breitner's Homepage
Today I held a lightning talk at the Karlsruhe Functional Programmer’s Group, where I presented “Real World Haskell” applications, i.e. programs that are written in Haskell, are somewhat mature and well-known and have non-programmers as their target group. Here is the (surely subjective) list that I have come up (also see the slides): darcs (since 2002, 35 000 loc): Distributed version control sys
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More thoughts on a bootstrappable GHC – Blog – Joachim Breitner's Homepage
More recursive definitions – Blog – Joachim Breitner's Homepage
Don’t think, just defunctionalize – Blog – Joachim Breitner's Homepage
Learn Haskell on CodeWorld writing Sokoban – Blog – Joachim Breitner's Homepage
Teaching to read Haskell – Blog – Joachim Breitner's Homepage
ghc-heap-view for GHC 7.8 – Blog – Joachim Breitner's Homepage
Another instance of Haskell Bytes – Blog – Joachim Breitner's Homepage
Does list fusion work? – Blog – Joachim Breitner's Homepage
https://www.joachim-breitner.de/publications/CallArity-TFP.pdf