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J.A. Alonso

Programming errors in traversal programs over structured data - 0 views

userpages.uni-koblenz.de/...syb42

artículo Haskell

shared by J.A. Alonso on 30 Jan 12 - No Cached
  • J.A. Alonso on 30 Jan 12
     
    Traversal strategies `a la Stratego (also `a la Strafunski and 'Scrap Your Boilerplate') provide an exceptionally versatile and uniform means of querying and transforming deeply nested and heterogeneously structured data including terms in functional programming and rewriting, objects in OO programming, and XML documents in XML programming. However, the resulting traversal programs are prone to programming errors. We are specifically concerned with errors that go beyond conservative type errors; examples we examine include divergent traversals, prematurely terminated traversals, and traversals with dead code. Based on an inventory of possible programming errors we explore options of static typing and static analysis so that some categories of errors can be avoided. This exploration generates suggestions for improvements to strategy libraries as well as their underlyingq programming languages. Haskell is used for illustrations and specifications with sufficient explanations to make the presentation comprehensible to the non-specialist. The overall ideas are language-agnostic and they are summarized accordingly.
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.
J.A. Alonso

Purely Functional Algorithm Specification ~ Jan van Eijck - 0 views

homepages.cwi.nl/...esslli12

curso haskell

shared by J.A. Alonso on 18 Aug 12 - No Cached
  • J.A. Alonso on 18 Aug 12
     
    This course offers a perspective on algorithm specification, in terms of purely functional programming. An algorithm is an effective method expressed as a list of instructions describing a computation for calculating a result. Algorithms have to be written in human readable form, either using pseudocode (natural language looking like executable code), a high level specification language like Dijkstra's Guarded Command Language, or an executable formal specification formalism such as Z. The course will develop a purely functional perspective on algorithm specification, and demonstrate how this can be used for specifying (executable) algorithms, and for automated testing of Hoare correctness statements about these algorithms. The small extension of Haskell that we will present and discuss can be viewed as a domain specific language for algorithm specification and testing. Inspiration for this was the talk by Leslie Lamport at CWI on the executable algorithm specification language PlusCal plus Edsger W. Dijkstra, "EWD472: Guarded commands, non-determinacy and formal derivation of programs." Instead of formal program derivation, we demonstrate test automation of Hoare style assertions.
J.A. Alonso

The Risks and Benefits of Teaching Purely Functional Programming in First Year - 0 views

www.cse.unsw.edu.au/...CK02a.html

artículo enseñanza programación haskell

shared by J.A. Alonso on 26 Nov 11 - Cached
  • J.A. Alonso on 26 Nov 11
     
    "We argue that teaching purely functional programming as such in freshman courses is detrimental to both the curriculum as well as to promoting the paradigm. Instead, we need to focus on the more general aims of teaching elementary techniques of programming and essential concepts of computing. We support this viewpoint with experience gained during several semesters of teaching large first-year classes (up to 600 students) in Haskell. These classes consisted of computer science students as well as students from other disciplines. We have systematically gathered student feedback by conducting surveys after each semester. This article contributes an approach to the use of modern functional languages in first year courses and, based on this, advocates the use of functional languages in this setting. "
Javier Neira

The best programming languages - 0 views

www.alpheccar.org/...36

smalltalk lisp haskell ruby analysis comparation

shared by Javier Neira on 11 Jan 10 - Cached
  • Haskell is not a programmable programming language (unless you look at extensions like template Haskell) but there are enough abstractions in Haskell to easily build domain specific languages with it.
  • But, the idea of time, the idea of sequencing can be built upon a purely functional system and we are led to monads
  • Monad are the recognition that the idea of sequencing operations can be formalized in a purely functional language.
  • ...2 more annotations...
  • The monad is an abstraction allowing to create new control structures and, in associations with the powerful type system of Haskell which makes possible elegant overloading of operators, it is possible to easily build new abstractions that allow to customize the programming language.
  • Unfortunately, Lisp, Smalltalk and Haskell are too different from most programming languages currently used in industry and taught in schools. They really look like alien technology to most developpers.
Javier Neira

A Neighborhood of Infinity: The IO Monad for People who Simply Don't Care - 0 views

blog.sigfpe.com/...or-people-who-simply-dont.html

haskell io monad basics intro

shared by Javier Neira on 22 Dec 09 - No Cached
  • Many programming languages make a distinction between expressions and commands.
  • Like other languages it makes the distinction, and like other languages it has its own slightly idiosyncratic notion of what the difference is. The IO monad is just a device to help make this distinction.
  • There is no room for anything like a print command here because a print command doesn't return a value, it produces output as a side-effect
  • ...18 more annotations...
  • It's easy to use: you just write do and then follow it by an indented list of commands. Here's a complete Haskell program:
  • Note also that commands take arguments that can be expressions. So print (2*x) is a command, but 2*x is an expression. Again, little different from a language like Python.
  • So here's an interesting feature of Haskell: commands can return values. But a command that returns a value is different from an expression with a value.
  • We have to use <- instead of let ... = ... to get a returned value out of a command. It's a pretty simple rule, the only hassle is you have to remember what's a command and what's a function.
  • get2Lines = do line1 <- getLine line2 <- getLine return (line1,line2)
  • To introduce a list of commands, use do.To return a value from a command, use return.To assign a name to an expression inside a do block use let.To assign a name to the result of a command, use <-.
  • what's a command and what's an expression? If it has any chance of doing I/O it must be a command, otherwise it's probably an expression.
  • Everything in Haskell has a type, even commands. In general, if a command returns a value of type a then the command itself is of type IO a.
  • eturn is simply a function of type a -> IO a that converts a value of type a to a command of type IO a.
  • 5. The type of a sequence of commands is the type of the last line.
  • The type of an if statement is the type of its branches. So if you want an if statement inside a do block, it needs to be a command, and so its branches need to be commands also. So it's
  • If something is of type IO a then it's a command returning an value of type a. Otherwise it's an expression. That's the rule.
  • following the rules above it's completely impossible to put an executed command inside an expression.
  • As the only way to do I/O is with commands, that means you have no way to find out what Haskell is doing inside expressions.
  • If the type isn't IO a, then you can sleep at night in the confidence that there are no side effects.
  • One last thing. Much of what I've said above is false. But what I hope I have done is describe a subset of Haskell in which you can start some I/O programming without having a clue what a monad is.
  • The idea of capturing imperative computations in a type of (immutable) values is lovely. And so is the general pattern we call "monad".
  • main = do return 1 print "Hello"
Javier Neira

What is (functional) reactive programming? - Stack Overflow - 0 views

stackoverflow.com/...1028250

reactive programming functional definition stackoverflow

shared by Javier Neira on 07 Jan 10 - Cached
  • Semantically, FRP's concurrency is fine-grained, determinate, and continuous.
  • Dynamic/evolving values (i.e., values "over time") are first class values in themselves. You can define them and combine them, pass them into & out of functions. I called these things "behaviors".
  • Each occurrence has an associated time and value.
  • ...3 more annotations...
  • In software design, I always ask the same question: "what does it mean?".
  • It's been quite a challenge to implement this model correctly and efficiently, but that's another story.
  • The basic idea behind reactive programming is that there are certain datatypes that represent a value "over time". Computations that involve these changing-over-time values will themselves have values that change over time.
Javier Neira

http://haskell.on-a-horse.org - 1 views

haskell.on-a-horse.org

haskel webdevv framework

shared by Javier Neira on 06 Sep 10 - Cached
  • Javier Neira on 06 Sep 10
     
    Haskell on a Horse (HoH) is a combinatorial web framework for the programming language Haskell.
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

Understanding Haskell Monads - 0 views

ertes.de/monads.html

haskell monads tutorial learning

shared by Javier Neira on 16 Dec 09 - Cached
  • The opposite of referentially transparent is referentially opaque. A referentially opaque function is a function that may mean different things and return different results each time, even if all arguments are the same.
  • a function that just prints a fixed text to the screen and always returns 0, is referentially opaque, because you cannot replace the function call with 0 without changing the meaning of the program.
  • n fact, a function, which doesn't take any arguments, isn't even a function in Haskell. It's simply a value. A number of simple solutions to this problem exist. One is to expect a state value as an argument and produce a new state value together with a pseudorandom number: random :: RandomState -> (Int, RandomState)
  • ...12 more annotations...
  • A general purpose language is almost useless, if you can't develop user interfaces or read files. We would like to read keyboard input or print things to the terminal.
  • We have seen that we can solve this problem by expecting a state argument. But what's our state? The state of the terminal?
  • We seem to have found a useful solution to our problem. Just pass the state value around. But there is a problem with this approach.
  • A very special feature of Haskell is the concept of generalization. That means, instead of implementing an idea directly, you rather try to find a more general idea, which implies your idea as a special case.
  • However, the traditional programmer never had to face generalization. At most they faced abstraction,
  • they are a very abstract structure, which allows implementing functionality at an incredibly general level.
  • Haskell [1] is a purely functional programming language. Functions written in it are referentially transparent. Intuitively that means that a function called with the same arguments always gives the same result.
  • askell takes another approach. Instead of passing the world state explicitly, it employs a structure from category theory called a monad.
  • They are an abstract structure, and at first it can be difficult to understand where they are useful. The two main interpretations of monads are as containers and as computations.
  • The ⊥ value is a theoretical construct. It's the result of a function, which never returns, so you can't observe that value directly. Examples are functions, which recurse forever or which throw an exception. In both cases, there is no ordinary returning of a value.
  • Now that Nothing is a valid result, our function handles all cases.
  • You have some computation with a certain type of result and a certain structure in its result (like allowing no result, or allowing arbitrarily many results), and you want to pass that computation's result to another computation.
Javier Neira

Bluish Coder: Dynamic Compilation and Loading of Modules in Haskell - 0 views

www.bluishcoder.co.nz/...ompilation-and-loading-of.html

haskell ghc dynamic compilation howto

shared by Javier Neira on 09 Dec 09 - Cached
  • Javier Neira on 09 Dec 09
     
    The Haskell system GHC has libraries that provide the ability to compile Haskell code and dynamically load it into a running Haskell program. A library that provides this functionality is hs-plugins. Unfortunately hs-plugins doesn't work with the latest GHC release, 6.10.1.
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.
Javier Neira

mwotton's Hubris at master - GitHub - 0 views

github.com/Hubris

ruby haskell interop bridge

shared by Javier Neira on 30 Nov 09 - Cached
  • Javier Neira on 30 Nov 09
     
    Hubris is a bridge between Ruby and Haskell, between love and bondage, between slothful indolence and raw, blazing speed. Hubris will wash your car, lie to your boss, and salvage your love life. If you are very, very lucky, it might also let you get some functional goodness into your ruby programs through the back door.
J.A. Alonso

Programming with effects - 0 views

www.cs.nott.ac.uk/monads

Tutorial Haskell

shared by J.A. Alonso on 01 Feb 12 - No Cached
  • J.A. Alonso on 01 Feb 12
     
    Introducción a las mónadas en Haskell.
mesbah095

Guest Post Online - 0 views

guestpostonline.com

haskell del.icio.us imported Tutorial functional programming reference intro monads howto

shared by mesbah095 on 03 Apr 14 - No Cached
  • mesbah095 on 03 Apr 14
     
    Article Writing & Guestpost You Can Join this Site for Your Article & guest post, Just Easy way to join this site & total free Article site. This site article post to totally free Way. Guest Post & Article Post live to Life time only for Current & this time new User. http://guestpostonline.com
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