N-ary Functors
Code and ideas in computer science. And maybe a short story or two. update: Now available on hackage as n-ary-functor. Functor and Bifunctor are both in base, but what about Trifunctor? Quadrifunctor? There must be a better solution than creating an infinite tower of typeclasses. Here's the API I managed to implement: > nmap <#> (+1) <#> (+2) $ (0, 0) (1,2) > nmap <#> (+1) <#> (+2) <#> (+3) $ (0,
Two kinds of backtracking
Code and ideas in computer science. And maybe a short story or two. I sometimes write my own parser combinators. I sometimes make mistakes while implementing my own parser combinators. In this post, I describe a mistake I made a few times: using the wrong kind of backtracking effect. 2015-08-11 update: it turns out everything in this post is already well-known in the litterature, see the Reddit di
Will it memoize?
Code and ideas in computer science. And maybe a short story or two. In this post, I will try several variants of a simple memoizing Haskell program and test whether the program actually memoizes or not. This will give us a better grasp on sharing. FibonacciIf you've been studying Haskell for any length of time, you have probably already stumbled upon the following unusual definition of the Fibonac
Strongly-typed ghci commands
Code and ideas in computer science. And maybe a short story or two. The ghci documentation explains how to implement conditional breakpoints by conditionally generating ghci commands depending on the values of variables which are in scope at the breakpoint. The approach works, but is hard to implement correctly because ghci's commands are stringly-typed. In this post, I will present a strongly-typ
Haxl anti-tutorial
Code and ideas in computer science. And maybe a short story or two. It's time for another anti-tutorial! Whereas a tutorial is an advanced user giving step-by-step instructions to help newbies, an anti-tutorial is a new user describing their path to enlightenment. My approach is usually to follow the types, so my anti-tutorials are also examples of how to do that. Previously in the series: pipes a
Prisms lead to typeclasses for subtractive types
Code and ideas in computer science. And maybe a short story or two. In my last post, I identified some issues with subtractive types, namely that math identities such as ∀ a. a + -a = 0, once they are translated into Haskell, would not be valid for all a. More precisely, the existence of a function of type cancelSub :: forall a. (a :+: Negative a) -> Zero would make it easy to implement a contradi
Homemade FRP: a study in following the types
Code and ideas in computer science. And maybe a short story or two. I wonder how FRP is implemented? Since I only know about a small part of reactive-banana so far, this is the interface I am currently thinking of when I think of FRP: data Event t a data Behavior t a instance Functor (Event t) instance Functor (Behavior t) instance Monoid (Event t) instance Applicative (Behavior t) filterE :: (a -
reactive-banana anti-tutorial
Code and ideas in computer science. And maybe a short story or two. This is not a tutorial. I have never used reactive-banana nor any other FRP library. And that's the point: in this post, once again1, I will reveal my thought process as I learn this library. Motivation A recent tutorial called The introduction to Reactive Programming you've been missing made me realize that FRP is no longer a nic
Comonads are neighbourhoods, not objects
Code and ideas in computer science. And maybe a short story or two. Gabriel Gonzalez, the author of the well-known pipes package, has written a blog post in which he claims that comonads are objects. I think he is mistaken, but I can't blame him; I used to be quite confused about comonads myself. Comonads are not objectsTo motivate the purported equivalence between objects and comonads, Gabriel gi
1
リリース、障害情報などのサービスのお知らせ
最新の人気エントリーの配信
j次のブックマーク
k前のブックマーク
lあとで読む
eコメント一覧を開く
oページを開く
The "99 Bottles of Beers" of Type Systems
The Commutativity monad