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Javier Neira

Learning Haskell Notes - 0 views

www.ninebynine.org/...Learning-Haskell-Notes.html

haskell learning notes

shared by Javier Neira on 09 Dec 09 - Cached
  • 8. Functors
  • A "functor" is a structured collection (or container) type with a method (fmap) that accepts a method and applies that method to the members of the collection yielding an isomorphic collection of values of a (possibly) new type. Is this right?
  • Every monad is a functor, but not the other way around; a monad is a functor PLUS functions >>= and return satisfying some laws
  • ...4 more annotations...
  • a functor is a type constructor PLUS a function fmap satisfying some laws.
  • I think it's better to use existentials, as they let you define multiple instances for the same type.
  • People tend to forget that the major difference between ADT's and OO-style classes is really only that with a class you can have many instances in the same program simultaneously, whereas with an ADT you can have only one; but the ADT implementation is still interchangeable.
  • sequence :: Monad m => [m a] -> m [a]
Javier Neira

Smart constructors - HaskellWiki - 0 views

www.haskell.org/...Smart_constructors

type haskell constructor restriction

shared by Javier Neira on 24 Jan 10 - Cached
  • The most interesting are probably the static checks that can be done with Type arithmetic, that enforce the number of bands at compile time, rather than runtime, by lifting the band count into the type level.
  • typecheck perform the check statically, using phantom types and Peano numbers.
  • So encode a type-level version of the bounds check. Only resistors with bands >= 4 and <= 8 are valid:
  • ...1 more annotation...
  • Further checks can be obtained by separating the metal and ceramic values on the type level, so no function that takes a metal resistor can be accidentally passed a ceramic one. A newtype is useful for this:
Javier Neira

Monads in 15 minutes: Backtracking and Maybe - 0 views

www.randomhacks.net/...monads-in-15-minutes

monads haskell backtracking howto

shared by Javier Neira on 09 Nov 09 - Cached
  • type Choice a = [a] choose :: [a] -> Choice a choose xs = xs
  • Because Haskell doesn’t compute answers until we ask for them, we get the actual backtracking for free!
  • The missing function is almost too trivial to mention: Given a single value of type a, we need a convenient way to construct a value of type Choice a:
  • ...5 more annotations...
  • More math trivia: return is also known as unit and η. That’s a lot of names for a very simple idea.)
  • makePairs = choose [1,2,3] >>= (\x -> choose [4,5,6] >>= (\y -> return (x,y)))
  • makePairs' = do x <- choose [1,2,3] y <- choose [4,5,6] return (x,y)
  • Every monad has three pieces: return, map and join.
  • Backtracking: The lazy way to code
Felipp Crawly

Amazing Customer Service - 1 views

I would like to thank Onward Process Solutions for greatly helping me with my need for assistance in a Customer service outsourcing project. They provided me with 24/7 phone/ email answering serv...

started by Felipp Crawly on 31 Oct 12 no follow-up yet
Justin Pierce

Tested And Trusted Bookkeeping Service - 1 views

When I opened my mini grocery last year, I immediately asked Bookkeepers On Call to do the bookkeeping services for me because I know it from my sister that they provide the most trusted bookkeeper...

started by Justin Pierce on 29 Oct 12 no follow-up yet
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)
J.A. Alonso

Foundations of Functional Programming - bu Robin Cockett - 0 views

pages.cpsc.ucalgary.ca/...webnotes.html

curso haskell i1m

shared by J.A. Alonso on 06 Oct 11 - No Cached
  • J.A. Alonso on 06 Oct 11
     
    The purpose of the course is to explore various aspects of functional programming using Haskell. In particular, the course provides an introduction to the lambda calculus, types in programming, and the role of these in the implementation of functional programming.
Javier Neira

The Haskell 98 Library Report: Arrays - 0 views

www.haskell.org/...array.html

haskell library Array reference

shared by Javier Neira on 10 Nov 09 - Cached
  • 16.2  Incremental Array Updates The operator (//) takes an array and a list of pairs and returns an array identical to the left argument except that it has been updated by the associations in the right argument. (As with the array function, the indices in the association list must be unique for the updated elements to be defined.) For example, if m is a 1-origin, n by n matrix, then m//[((i,i), 0) | i <- [1..n]] is the same matrix, except with the diagonal zeroed.
  • -- A rectangular subarray subArray :: (Ix a) => (a,a) -> Array a b -> Array a b subArray bnds = ixmap bnds (\i->i) -- A row of a matrix row :: (Ix a, Ix b) => a -> Array (a,b) c -> Array b c row i x = ixmap (l',u') (\j->(i,j)) x where ((_,l'),(_,u')) = bounds x -- Diagonal of a matrix (assumed to be square) diag :: (Ix a) => Array (a,a) b -> Array a b diag x = ixmap (l,u) (\i->(i,i)) x        where           ((l,_),(u,_)) = bounds x -- Projection of first components of an array of pairs firstArray :: (Ix a) => Array a (b,c) -> Array a b firstArray = fmap (\(x,y)->x)
mountain

Pipes: del.icio.us popular links for programming - 0 views

pipes.yahoo.com/...pipe.info

c++ calm del.icio.us dsl erlang haskell imported javascript meta metaprograming ml ocaml perl php rails ruby schema smalltalk stm

shared by mountain on 24 Jun 07 - Cached
  • mountain on 24 Jun 07
     
    del.icio.us popular links for programming, inculding java, c++, smalltalk, ruby, haskell, ml, schema, calm, ocaml, php, erlang, rails, perl, STM, metaprograming, and DSL
Javier Neira

Existential type - HaskellWiki - 0 views

www.haskell.org/...Existential_type

ghc type existential

shared by Javier Neira on 21 Dec 09 - Cached
  • First of all, it is now impossible for a function to demand a Worker having a specific type of buffer. Second, the type of foo can now be derived automatically without needing an explicit type signature. (No monomorphism restriction.) Thirdly, since code now has no idea what type the buffer function returns, you are more limited in what you can do to it.
  • This illustrates creating a heterogeneous list, all of whose members implement "Show", and progressing through that list to show these items: data Obj = forall a. (Show a) => Obj a   xs :: [Obj] xs = [Obj 1, Obj "foo", Obj 'c']   doShow :: [Obj] -> String doShow [] = "" doShow ((Obj x):xs) = show x ++ doShow xs With output: doShow xs ==> "1\"foo\"'c'"
  • Existential types in conjunction with type classes can be used to emulate the dynamic dispatch mechanism of object oriented programming languages. To illustrate this concept I show how a classic example from object oriented programming can be encoded in Haskell.
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