# Articles and papers (January 2015)

Posted on January 15, 2015

This post provides a list of the coolest articles and papers read by me during January 2015. Currently, this post is a work in progress.

### Apfelmus, H. 2009. Monoids and Finger Trees

This is a blog-post about using monoid to turn annotated binary tree into a data-structures-Swiss-army-knife. Main idea is that because often tag (annotation) of a branch is, practically, a function of annotations of its children:

annotation v a ∷ Tree v a → v
annotation (Branch _ x y) = f (annotation x) (annotation y)
annotation (Leaf   _ a)   = measure a

where f fits axioms of mappend and v so often behaves like Monoid, Apfelmus, citing Hinze, R. and Patterson, R. offers following generalization:

class Monoid v ⇒ Measured a v where
measure ∷ a → v

branch ∷ Monoid v ⇒ Tree v a → Tree v a → Tree v a
branch x y = Branch ((annotation x) ◇ (annotation y)) x y

leaf ∷ Measured a v ⇒ a → Tree v a
leaf a = Leaf (measure a) a

### Bruno, L. 2014/15. Nix Pills

Luca is doing important job of covering grounds of interactive documentation for Nix package manager and NixOS.

Nix pills start with trivial stuff, like language overview and basic expressions and are taking reader to an entertaining ride through some specific parts of Nix workflows that might be obscure for a Nix newcomer.

The design of the blog is pretty terrible (see initial callPackage definition in this post), but with w3m or lynx, it’s pretty readable.

### Drake, A. 2014. Command-line tools can be 235× faster than your Hadoop cluster

A great post that boils down to the simple notion of choosing the right tool for the job, hinting the need of hiring experienced software architects and doing R&D properly (not following the hype).

### Volkov, N. 2015. Announcing the first class records library

Based on Volkov, N. 2013. Anonymous records. A solution to the problems of record-system. proposal, Nikita Volkov suggests using type-level string literals to build a library, capable of quite sexy things, like

type Person =
[r| {name ∷ String,
birthday ∷ {year ∷ Int, month ∷ Int, day ∷ Int},
country ∷ Country} |]

type Country =
[r| {name ∷ String,
language ∷ String} |]

person ∷ Person
person =
[r| {name = "Yuri Alekseyevich Gagarin",
birthday = {year = 1934, month = 3, day = 9},
country = {name = "Soviet Union", language = "Russian"}} |]

A subset of lens are integrated with Volkov’s records:

getPersonBirthdayYear ∷ Person → Int
getPersonBirthdayYear =
view ([l|birthday|] . [l|year|])

setPersonBirthdayYear ∷ Int → Person → Person
setPersonBirthdayYear =
set [l|birthday.year|]

There’s a long way to go for this library, but I really hope for a standard and sane records in Haskell.

That’s why you read maling lists, not wiki, people. Awesome article by Peter Simons, providing up-to-date information regarding setting up Haskell environment(s). Helped me to organize my environment.

#### Simons, P. 2014. Haskell NG

Peter explains what haskellngPackages are, which problems they solve and why you should go to nixpkgs and mark stuff that doesn’t build as broken (at least).

Good article to read, to get a perspective of Haskell NG development.

#### Simons, P. 2015. A Journey into the Haskell NG infrastructure: Part II

FAQ about state of the art of Haskell NG and why should we care. Explains provideOldHaskellAttributeNames, explains why did ghc-wrapper disappear for good and much more. Prototype for new Nix Haskell documentation.

Even though at the moment of writing I’m not sure if I can successfully build yesod and yi on my computer with nix, I have a clear picture of what I should do next. When I accomplish that, be sure that I’ll write a blog post about it.

Added, Jan 25th — turns out, haskellng is great for libraries that aren’t inherently broken (read: for major Haskell libraries and applications that don’t follow Yesod’s distribution pattern). Besides, Pete Simons is really fast on fixing bugs in haskellng expressions. I’m a little bit shy to send PRs myself yet though.

### Zovic, L. 2013. Wai Without Yesod - Simple Example of Haskell Web Development

In this post, Leo rolls out a Yesod-less grocery shopping listing application. What I love about this blog-post (and most of his blog-posts) is that it has this “get things done” attitude. Don’t expect production-grade code there, however it’s a very nice and gentle introduction into the world of WAI.

### Simmons, B. 2014. Announcing Unagi-chan

I found this article somewhat related to the talk, given by Paolini-Subramanya, M. at Erlang User Conference in 2013 (that I had an honour to witness in person). There Mahesh was talking about the practical sides of queue management and why in real high-load systems it’s absolutely critical to get less wrong. In that sense, some of theoretical insights given by Brandon.

The source code of this library is a nice study in queues, definitely worth looking at.