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The big problem I've had with Haskell is that even after gaining a pretty good understanding of the language (including monads and such) I still can't fathom ho

• sotojuan 9y ago
  > The big problem I've had with Haskell is that even after gaining a pretty good understanding of the language (including monads and such) I still can't fathom how to do anything real with it I agree with you but the book has chapters where you write a URL shortener and the final project is an implementation of the `finger` Unix command. For me, the book was a stepping stone towards materials like Write You a Scheme (Scheme interpreter in Haskell). I will admit though, I read Haskell Book for the ideas and learning typed functional programming. I wasn't planning on using Haskell everyday for projects.
• marcosdumay 9y ago
  Try doing everything in IO, passing stuff around by hand and ignoring all that abstraction. You will immediately spot some places where a monad will help you. Where that happens, use the monad, elsewhere, keep it simple. With time you will regret some of that simple code, when that happens, change it (Haskell's best use case is on refactoring). With even more time you'll get a taste for where it's good to go complex from the start.
• cstrahan 9y ago
  I'd recommend just making yourself pick up a project, and run with it. Try not to over think it, and if you start to feel paralyzed, just say "fuck it, I'll do it the first, shittiest way that comes to mind." As an example, the first "real" project I wrote in Haskell was one or two weeks into learning it: a web testing framework/DSL (a la Capybara[0]) that spoke a (custom) protocol over socket to a headless webkit instance[1]. Looking back, I abused stuff like type-classes and such, but then again, it was all a learning experience. I should probably be a little embarrassed about how I left the project, but in the interest of providing some inspiration, here it is in all its gory -- I mean, glory: https://github.com/cstrahan/happybara https://github.com/cstrahan/happybara [0]: http://teamcapybara.github.io/capybara/ http://teamcapybara.github.io/capybara/ [1]: https://github.com/thoughtbot/capybara-webkit/tree/master/src https://github.com/thoughtbot/capybara-webkit/tree/master/sr...
  • laumars 9y ago
    I completely agree with the "write shit code" approach. That's how I learn any new language. As long as you adopt an attitude where you are aware that you're writing bad code and are willing to adapt and learn better processes as you progress, then it's the quickest way to getting proficient. Much like that immersion technique of learning a foreign language by moving to another language.
    • problems 9y ago
      Yeah, the key is to start out writing shit code, but to skim over and get a feel for when you might use the more advanced concepts so that when the time comes that you think you might be able to apply something you know what to look for quickly.
  • jcadam 9y ago
    > I'd recommend just making yourself pick up a project, and run with it. Try not to over think it, and if you start to feel paralyzed, just say "fuck it, I'll do it the first, shittiest way that comes to mind." I tried that. When I got stuck (fairly early on), I ended up switching my project from Haskell to Clojure :/
• Sean1708 9y ago
  Write Yourself A Scheme[0]? It's a fairly big project for a tutorial so it might be a good next stage for you. [0]: https://en.wikibooks.org/wiki/Write_Yourself_a_Scheme_in_48_Hours https://en.wikibooks.org/wiki/Write_Yourself_a_Scheme_in_48_...
• mrkgnao 9y ago
  Bonsoir, allow me to introduce Servant. http://haskell-servant.readthedocs.io/en/stable/index.html http://haskell-servant.readthedocs.io/en/stable/index.html Servant allows you to write a type that describes a server/API, and automatically derives a specification for it. You can then write handlers for the different API endpoints, and it will only compile if every endpoint is correctly handled. That includes content types, status codes, and so on, everything is verified, and things are often derived for you. All (de)serialization to/from JSON is automatic (although you can write your own instances if you want your JSON to look a certain way). For example, from the Servant docs: type API = "position" :> Capture "x" Int :> Capture "y" Int :> Get '[JSON] Position :<|> "hello" :> QueryParam "name" String :> Get '[JSON] HelloMessage :<|> "marketing" :> ReqBody '[JSON] ClientInfo :> Post '[JSON] Email This is equivalent to an API that defines these three endpoints: GET /position/:x/:y/ returns a Position object as JSON GET /hello?name=whatever returns a HelloMessage object as JSON POST /marketing given a JSON request that represents a ClientInfo object, returns an Email object as JSON but the spec is code: code that the compiler can check for you! You can then write functions of the following types handlePosition :: Int -> Int -> Handler Position handleHello :: Maybe String -> Handler HelloMessage handleMarketing :: ClientInfo -> Handler Email where "Handler thing" effectively means that you can do something like write to a log or throw an exception while you return the thing. This will typecheck, and you have a server that must do what it says on the "tin", the tin being the API type above. If you add a new API endpoint, and forget to write a Handler for it, you'll get to know. If you change the Position type to work with x, y, and z coordinates but forget to update your handlers, you'll get to know. If you'd like to also allow clients to request HTML instead for some endpoint, just change the '[JSON] to '[JSON,HTML]. The Haskell typesystem will make sure that someone requesting a text/html Content-Type doesn't get hit with a 500 or something. Note the Maybe String there: if you wrote a handler for the /hello endpoint that had the type String -> Handler HelloMessage, Servant would complain: you're expecting a query parameter, which the client doesn't have to provide. This is in stark contrast to, say, the "NoneType has no attribute whatever" problems that one risks having to face with Django: if it compiles, it meets the spec. Of course, static typing won't prevent you from responding to /hello with Lovecraft quotes. -- > I start getting lost in layers of monad transformers Handler is actually a monad transformer, and it's a great first one: it's essentially[0] type Handler a = ExceptT ServantErr (ReaderT Config IO) a if memory serves, which means that a "Handler a" is a computation that can * throw a ServantErr * read values from a Config object * perform IO actions (read files, make other network requests, log things, "fire missiles") when run, returning a value of type a. Anecdotally, monad transformers never clicked for me until I started muddling through actually using them in code like this. After a couple of months, you realise it's not too wrong to say you understand how to use them, and you slowly begin to be able to rely on the type system for support. Libraries like Servant are a great example of how this can really, really help. I stopped to think last week how similar it is to pair-programming with a really intelligent but sometimes obtuse friend who likes pointing out how "this doesn't follow from your assumptions", all the way from > "Wait, but you can't add two books together." to > "What if someone PUTs to /login?" which is what we had above, to > "And what happens if I try to withdraw all my money exactly when the payment I've made to you is getting executed?" (in this case, you discover the wonders of software transactional memory[1]). A better typesystem allows you to let the compiler handle more of the busywork that you'd originally have written tests or comments for. It is sometimes confusing starting out (when one discovers that 3 isn't an Int, but a "Num a => a", for instance), but it gets better. Once you get past the Project Euler/"look ma, infinite lists!" stuff, "real" Haskell does have a tendency to make people underestimate how much they really know, but as I've discovered, taking the plunge reveals that one has progressed much farther than one thinks. Also, #haskell on Freenode is one of the friendliest places I've encountered on the internet[0]. [0]: http://haskell-servant.readthedocs.io/en/stable/tutorial/Server.html#the-handler-monad http://haskell-servant.readthedocs.io/en/stable/tutorial/Ser... [1]: https://www.schoolofhaskell.com/school/advanced-haskell/beautiful-concurrency/3-software-transactional-memory https://www.schoolofhaskell.com/school/advanced-haskell/beau... [2]: Here's a hilarious example (NSFW language warning): https://gist.github.com/quchen/5280339 https://gist.github.com/quchen/5280339 -- Other stuff: Corrode is a C-to-Rust converter written in literate Haskell (as in, it's like a blog post that you can compile and run, to give a slightly strained analogy). https://github.com/jameysharp/corrode https://github.com/jameysharp/corrode webshit weekly actually "quoted" a previous HN comment of mine about it, in which I was falsely slandered: I'm not a Rust evangelist! I wrote a small "script" to make tmux status bars a while back that was a good example of how fun "scripting"-style thing can be in Haskell. https://github.com/mrkgnao/remux https://github.com/mrkgnao/remux And there's always XMonad!
• icc97 9y ago
  Surely just do what ever you'd try to do with another language but just use Haskell instead. Depends on how complex you want to do things. You can just use yesod [0] to create a web app and compare it to an existing one you'd written. An interesting use of Haskell is with concurrency [1], so anything along those lines should give you something pretty awesome. [0]: http://www.yesodweb.com/ http://www.yesodweb.com/ [1]: http://chimera.labs.oreilly.com/books/1230000000929/index.html http://chimera.labs.oreilly.com/books/1230000000929/index.ht...
• deleted 9y ago
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• m8rrsnt 9y ago
  I second this. Learning less popular languages, you drive off a cliff when you get to the intermediate stage. I wasted a lot of time because I didn't which language extensions (developed over last the 20 years but never added to the base language) and modules are generally seen as essential. Books and web tutorials didn't talk much about them, but the real world was different. I was like I was thrown out the tutorial-door into a wide world of questionable documentation and implicit knowledge known only by wizards in IRC, if ye dare idle to find 'em.
  • mrkgnao 9y ago
    If you use a good "IDE" setup, it'll tell you what extensions you should enable for some code to compile. Intero (on Emacs) allows you to hit C-c C-r to insert the relevant incantation at the top of the file. About what extensions people consider kosher, Stephen Diehl's "What I Wish I Knew When Learning Haskell" has a great list that sorts them into "common", "uhh", and "you obviously know what you're doing".
• nightski 9y ago
  I wrote a 3D mesh reconstruction algorithm using feature point extraction in Haskell. The hardest part was graph algorithms since those can be pretty tricky to express in functional languages. But Even with 3D output to OpenGL, image loading and manipulation, etc.. I never touched a monad transformer. I think you are trying too hard. Just embrace IO for the effects and move everything else to pure code.
• dualogy 9y ago
  > I still can't fathom how to do anything real with it That's incredibly easy, of your list of "problems to attack and programs to write some time soon" pick any one and get busy. It'll feel real-world very soon and there's no better way to grasp "real-world Haskell". The first iteration will be ugly, but on the plus side you'll notice that yourself and that's quite some progress already. Keep at it a bit more and perceived "decent post-newb proficiency" is within reach. Well-rounded mature libraries for "real-world periphery" (DBs, json/yaml/html/xml/all that jazz) abound, too. What I find much more annoying is the lack of freelance projects. It's literally the language of academics, hobbyists, weekenders, late-nighters, githubbers. (Certainly also suitable for bootstrappers imho in a "Viaweb-Lisp-advantage" kinda way) If you want to avoid full-time employ, you're gonna have to keep doing .net/java/golang/node and such projects. Haskell code-bases I feel are private well-guarded silos within academia and a number of corps, no wider "projects ecosystem" to speak of.
• DonHopkins 9y ago
  I got some insight into what's great about Haskell by reading James Clark's "An algorithm for RELAX NG validation": http://www.thaiopensource.com/relaxng/derivative.html http://www.thaiopensource.com/relaxng/derivative.html This document describes an algorithm for validating an XML document against a RELAX NG schema. This algorithm is based on the idea of what's called a derivative (sometimes called a residual). It is not the only possible algorithm for RELAX NG validation. This document does not describe any algorithms for transforming a RELAX NG schema into simplified form, nor for determining whether a RELAX NG schema is correct. We use Haskell to describe the algorithm. Do not worry if you don't know Haskell; we use only a tiny subset which should be easily understandable.
• plinkplonk 9y ago
  Fwiw I have been writing production Haskell for years, am comfortable with Category Theory etc, and most of my code is still in "records and pure functions (that act on records)" style. You don't have to use the most esoteric constructs the language offers, or get into the weeds of how lenses work (just a random example of a seemingly 'esoteric' library) or language extensions to write code that does something useful. That said, a project centred Haskell book would be nice to have.