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Javier Neira

Applicative-what? Functor-who? « wxfz :: Blog - 0 views

wxfz.wordpress.com/...applicative-what-functor-who

haskell control structures functors arrows monads intro

shared by Javier Neira on 09 Sep 10 - No Cached
  • Monads Are  a kind of abstract data type used to represent computations (instead of data in the domain model).
Javier Neira

Fatvat: Web Sockets and Haskell - 0 views

www.fatvat.co.uk/...web-sockets-and-haskell.html

web socket haskell example toHack webdev

shared by Javier Neira on 05 Jan 10 - No Cached
  • Javier Neira on 05 Jan 10
     
    import Network import System.IO import Control.Concurrent import Char serverHandshake = "HTTP/1.1 101 Web Socket Protocol Handshake\r\n\ \Upgrade: WebSocket\r\n\ \Connection: Upgrade\r\n\ \WebSocket-Origin: http://localhost\r\n\ \WebSocket-Location: ws://localhost:9876/\r\n\ \WebSocket-Protocol: sample\r\n\r\n\0" acceptLoop socket = forever $ do (h,_,_) IO () listenLoop h = do sendFrame h "hello from haskell" threadDelay (3 * 1000000) sendFrame h "it works!" return () sendFrame :: Handle -> String -> IO () sendFrame h s = do hPutChar h (chr 0) hPutStr h s hPutChar h (chr 255)
Javier Neira

jaspervdj - Maybe, null, and boilerplate code - 0 views

jaspervdj.be/...04-maybe-null-boilerplate.html

haskell Maybe monad example

shared by Javier Neira on 05 Jan 10 - Cached
  • A first goal they serve is as "unassigned variables". I will not cover that here, instead I will focus on another use: abnormal return values.
  • So, null is some sort of "Not found" error here. But wait - they could have used an Exception here!
  • We see a similar behavior here: when the object is found, we get a Just a, and when it is not found, we get Nothing - comparable to a null pointer.
  • ...5 more annotations...
  • So, while we can get a null back from a function, we should never give it to a function.
  • Now, if you have written a lot of Java code, you know that checking for null is a vital part of the job, and fragments like the one above are pretty common.
  • In Haskell, however, Maybe is also a monad - and monads can be used to prevent common patterns in code - in other words, they assist you in the D.R.Y.-principle2. We can therefore write the above snippet again using do-notation3.
  • getPathMonth :: Map String String -> Maybe MonthgetPathMonth m = do p <- lookup "path" m d <- parseDate p return $ getMonth d
  • he whole "check-for-null-and-short-circuit" behavior is defined by the Maybe monad -
  • Javier Neira on 05 Jan 10
     
    getPathMonth :: Map String String -> Maybe Month getPathMonth m = case M.lookup "path" m of Nothing -> Nothing (Just p) -> case parseDate p of Nothing -> Nothing (Just d) -> Just (getMonth d) getPathMonth :: Map String String -> Maybe Month getPathMonth m = do p <- parseDate p return $ getMonth d
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