While explaining to someone what a type class X is I struggle to find good examples of data structures which are exactly X. So, I request examples for: A type constructor which is not a Functor. A type constructor which is a Functor, but not Applicative. A type constructor which is an Applicative, but is … Read more
I believe the Erlang community is not envious of Node.js as it does non-blocking I/O natively and has ways to scale deployments easily to more than one processor (something not even built-in in Node.js). More details at http://journal.dedasys.com/2010/04/29/erlang-vs-node-js and Node.js or Erlang What about Haskell? Can Haskell provide some of the benefits of Node.js, namely … Read more
I know you can convert a String to an number with read: Prelude> read “3” :: Int 3 Prelude> read “3” :: Double 3.0 But how do you grab the String representation of an Int value? 4 Answers 4
The two Haskell web frameworks in the news recently are Yesod (at 0.8) and Snap (at 0.4). It’s quite obvious that Yesod currently supports a lot more features than Snap. However, I can’t stand the syntax Yesod uses for its HTML, CSS and Javascript. So, I’d like to understand what I’d be missing if I … Read more
I’m learning Haskell and read a couple of articles regarding performance differences of Haskell lists and (insert your language)’s arrays. Being a learner I obviously just use lists without even thinking about performance difference. I recently started investigating and found numerous data structure libraries available in Haskell. Can someone please explain the difference between Lists, … Read more
Can Template Haskell find out the names and/or the declarations of the associated type synonyms declared in a type class? I expected reify would do what I want, but it doesn’t seem to provide all the necessary information. It works for getting function type signatures: % ghci GHCi, version 7.8.3: http://www.haskell.org/ghc/ 😕 for help … … Read more
It seems that Template Haskell is often viewed by the Haskell community as an unfortunate convenience. It’s hard to put into words exactly what I have observed in this regard, but consider these few examples Template Haskell listed under “The Ugly (but necessary)” in response to the question Which Haskell (GHC) extensions should users use/avoid? … Read more
I want to study FRP in Haskell, but it’s a bit difficult to decide on a library to use. Many seem to be dead attempts, some seem to have been resurrected (such as recent activity on Yampa). From what I read, it seems that there are two “kinds” of FRP: push-pull FRP (like in Reactive-banana … Read more
I came across the following definition as I try to learn Haskell using a real project to drive it. I don’t understand what the exclamation mark in front of each argument means and my books didn’t seem to mention it. data MidiMessage = MidiMessage !Int !MidiMessage 3 Answers 3
The ‘algebraic’ expression for algebraic data types looks very suggestive to someone with a background in mathematics. Let me try to explain what I mean. Having defined the basic types Product • Union + Singleton X Unit 1 and using the shorthand X² for X•X and 2X for X+X et cetera, we can then define … Read more
