May 2013 - Beginners - Haskell.org

Haskell on Debian
by Giacomo Tesio 26 May '13

26 May '13

Can I use cabal install without being root? I'd like to use packages from hackage instead of those provided by apt-get as far as possibile. Is it possible at all? I guess that libraries depending on FFI won't works... Giacomo

4 3

Lens and imperative programming
by Giacomo Tesio 24 May '13

24 May '13

Hi, I'm reading about the Lens package, and I'm scared by the imperative style that it enables. I know the limits of imperative programming, and despite the fact that lens are purely functional by themself, I'm scared about limits in readability of code. I'm afraid of writing "write-only" code. I guess I'm wrong, but I'd like to know your opinions. Giacomo

4 4

Functional JavaScript Opportunity in NYC
by Ryan Trinkle 22 May '13

22 May '13

Hi everyone, Our company, skedge.me, is looking for a full-time front-end developer in the NYC area. Our front-end is written in JavaScript, but our back-end is written in Haskell, so we're looking for people with solid JavaScript experience but also a strong interest in functional programming. No work experience in Haskell is required, but we do require all applicants to submit a small code sample - something on the scale of a Project Euler problem - in a statically-typed functional language in addition to a more traditional JavaScript code sample. We write all of our JavaScript in a functional style, and we use the Google Closure compiler to provide some type checking for us, so we're looking for people who enjoy working in an environment with a bit more structure than the average JavaScript project. For more information or to apply, visit http://skedge.me/careers or contact me at ryan(a)skedge.me. Ryan Trinkle

1 0

dismantling monolithic data structure
by Michael Litchard 22 May '13

22 May '13

This is in reference to an ongoing project, whose latest problem was articulated on stackoverflow: http://stackoverflow.com/questions/16484322/functional-banana-traveller-tim… While struggling with this problem, I realized the monlithlic style of GameState did not fit the FRP approach. This was also noticed by Heinrich, who advised me on steps to take to fix that. Here's a quote from StackOverflow I'd like to talk about. "First, looking at your code, I find it odd that you have "outsourced" the actual gameplay logic to the monolithic GameState type and the updateGSfunction. Now, this is not a bad thing to do, it's just that there is no benefit from using FRP in this style. You can remove the makeNetworkDescription function altogether and register an event handler with addCommandEvent by hand instead." He then goes on to offer some useful details that address the problem articulated in the question, which also gives a general approach about how to do this right. But first thing is first, getting rid of makeNetworkDescription. I'm trying to figure out how to register an event handler with addCommandEvent by hand. What functions and examples could I look at to get an idea of what to do?

1 0

Rewriting bits of a data structure
by Adrian May 21 May '13

21 May '13

Hi All, I have a lot of ugly code like this: data Thing = Thing Int Int Int Int Int rewriteFourth :: Int -> Thing -> Thing rewriteFourth x (Thing a b c _ e) = Thing a b c x e Is there a better way? It was thinking about state monads that reminded me of this junk that I'd already written a while ago. Maybe it can be done by applying five StateT transformers, but I'm not entirely sure how to write that, or if there's a simpler fix. TIA, Adrian.

3 4

ANN: MOOC course on Functional Programming
by Rustom Mody 21 May '13

21 May '13

We are offering the Haskell/FP related course: https://moocfellowship.org/submissions/the-dance-of-functional-programming-… which goes online if it gathers enough votes. It is our contribution towards getting Haskell and FP up on MOOC (Massive Open Online Course). The aim is: 1. To use Haskell as medium to understand and showcase functional programming 2. To show how using Haskell *as a thinking language* can change the quality of programming in more conventional *coding languages* -- eg python. It has been designed in the spirit of using haskell to play with ideas, and then idiomatically refine them for any implementation contexts including Haskell. Therefore, in this course (classical) typeful functional programming will take precedence over (modern) 'type hackery'. Some aspects of this shift of emphasis is [3]. Also some paradigm/philosophy questions, eg why much-hyped paradigms like OOP are not such a good idea [4] Functional Programming has never had it so good as today! Books like RWH, implementations like ghc, and of course the Haskell language itself are all part of this 'Never Before.' spj has often joked about 'avoiding success at all costs'. This may be somewhat tongue-in-cheek yet is also serious. As Haskell enters the mainstream and begins to compete head-on-head with C, C++, Java, Python etc, we need to separate out these aspects: 1. Mastering Haskell is harder today than when FP was an academic passtime 2. *Haskell-the-technology* is obscuring the possibilities and reach of * Haskell-for-CS *3. The elegant computer science (FP) + powerful modern technology (ghc) is obscuring the questions of paradigm and perspective that marked the inception of the field in an earlier era [1] One of the main intentions behind this course is to take cognizance of these facts and work on the Haskell-learning-curve to make it accessible to people with a wide swathe of interests/backgrounds. So… Those who are called to the above, Please Vote! And those who are not called, also please vote [After all the choice is between this Haskell/FP course and none <wink> ] Rusi ----------------------------- [1] Think of AI → Lisp, Denotational Semantics → ML, Notation as a tool for thought → APL etc [2] https://moocfellowship.org/submissions/the-dance-of-functional-programming-… [3] A shopping-list of topics in 'classic FP' : http://blog.languager.org/2012/10/functional-programming-lost-booty.html Recursion as a wider concept than just recursive functions http://blog.languager.org/2012/05/recursion-pervasive-in-cs.html [4] Folly of OOP http://blog.languager.org/2012/07/we-dont-need-no-ooooo-orientation-4.html

2 2

Re: [Haskell-beginners] ANN: MOOC course on Functional Programming
by 7stud 20 May '13

20 May '13

I don't get it. Is that a class being offered online? Is it free? When is it offered? -----Original Message----- From: "Rustom Mody" [rustompmody(a)gmail.com] Date: 05/19/2013 12:37 PM To: "beginners" <beginners(a)haskell.org> Subject: [Haskell-beginners] ANN: MOOC course on Functional Programming We are offering the Haskell/FP related course: https://moocfellowship.org/submissions/the-dance-of-functional-programming-… which goes online if it gathers enough votes. It is our contribution towards getting Haskell and FP up on MOOC (Massive Open Online Course). The aim is: 1. To use Haskell as medium to understand and showcase functional programming 2. To show how using Haskell as a thinking language can change the quality of programming in more conventional coding languages -- eg python. It has been designed in the spirit of using haskell to play with ideas, and then idiomatically refine them for any implementation contexts including Haskell. Therefore, in this course (classical) typeful functional programming will take precedence over (modern) type hackery. Some aspects of this shift of emphasis is [3]. Also some paradigm/philosophy questions, eg why much-hyped paradigms like OOP are not such a good idea [4] Functional Programming has never had it so good as today! Books like RWH, implementations like ghc, and of course the Haskell language itself are all part of this Never Before. spj has often joked about avoiding success at all costs. This may be somewhat tongue-in-cheek yet is also serious. As Haskell enters the mainstream and begins to compete head-on-head with C, C++, Java, Python etc, we need to separate out these aspects: 1. Mastering Haskell is harder today than when FP was an academic passtime 2. Haskell-the-technology is obscuring the possibilities and reach of Haskell-for-CS 3. The elegant computer science (FP) + powerful modern technology (ghc) is obscuring the questions of paradigm and perspective that marked the inception of the field in an earlier era [1] One of the main intentions behind this course is to take cognizance of these facts and work on the Haskell-learning-curve to make it accessible to people with a wide swathe of interests/backgrounds. So… Those who are called to the above, Please Vote! And those who are not called, also please vote [After all the choice is between this Haskell/FP course and none <wink> ] Rusi ----------------------------- [1] Think of AI → Lisp, Denotational Semantics → ML, Notation as a tool for thought → APL etc [2] https://moocfellowship.org/submissions/the-dance-of-functional-programming-… [3] A shopping-list of topics in classic FP : http://blog.languager.org/2012/10/functional-programming-lost-booty.html Recursion as a wider concept than just recursive functions http://blog.languager.org/2012/05/recursion-pervasive-in-cs.html [4] Folly of OOP http://blog.languager.org/2012/07/we-dont-need-no-ooooo-orientation-4.html

4 4

Re: [Haskell-beginners] Fish tank monad
by Stephen Tetley 18 May '13

18 May '13

Are you wanting to draw schedules or calculate them? Calculating schedules is a model problem within the logic programming community - a language like Oz might be better suited to the task than Haskell (Oz having more developed infrastructure and literature in this area).

2 1

installing text-icu on Mac OSX with cabal
by 7stud 18 May '13

18 May '13

I want to try unicode with haskell, and the Data.Text docs say I need text-icu. This is what I tried: Mac OS X 10.6.8 ~/haskell_programs$ cabal update Downloading the latest package list from hackage.haskell.org ~/haskell_programs$ cabal install text-icu Resolving dependencies... Downloading text-icu-0.6.3.5... Configuring text-icu-0.6.3.5... cabal: Missing dependencies on foreign libraries: * Missing C libraries: icui18n, icudata, icuuc This problem can usually be solved by installing the system packages that provide these libraries (you may need the "-dev" versions). If the libraries are already installed but in a non-standard location then you can use the flags --extra-include-dirs= and --extra-lib-dirs= to specify where they are. Failed to install text-icu-0.6.3.5 cabal: Error: some packages failed to install: text-icu-0.6.3.5 failed during the configure step. The exception was: ExitFailure 1 I found a post by a Windows user who had the same problem. Do I really need to go out and install those C libraries? Or are they 'misplaced' somewhere on my system? Thanks.

3 2

Fish tank monad
by Adrian May 18 May '13

18 May '13

Hi folks, I think I need a monad but I'm not sure which, and maybe something simpler would do. I want to model a fish tank as a function of time onto how many fish there are in it at that time. If I already have such a function, I want to operate on it with something like "add 2 fish on day 20" or "take 3 away on day 15" to get a new function of the same form, but the latter should not remove more fish than there are in the tank at that time, and it should tell me how many I get. I don't promise to apply these operators in chronological order. This seems like the kind of thing that would be in the prelude somewhere. But where? TIA, Adrian.

3 3