A functional programming language

learn more… | top users | synonyms

3
votes
2answers
691 views

Haskell syntax for type definitions: why the equality sign?

I am a bit confused by the choice of Haskell syntax for type definitions, like in data Foo = Bar Namely: does the equality sign here really mean an equality in some subtle sense, or is it just a ...
4
votes
2answers
408 views

How do you handle specific networking exceptions in Haskell?

I have the following to try and connect to a server: testAddress :: HostName -> Int -> IO (Maybe Handle) testAddress host iPort = do let port = PortNumber $ fromIntegral iPort putStrLn ...
2
votes
1answer
401 views

Difference between Yesod and Ocsigen web frameworks [closed]

I have been looking at web-frameworks in functional languages and eventually found Yesod and Ocsigen interesting. As far as I understand, they leverage the type system to statically prevent basic ...
10
votes
0answers
242 views

Why do Haskell functors only have derived types in their target category?

In Haskell, the Functor typeclass functor is defined as follows (see e.g. Haskell wiki): class Functor (f :: * -> *) where fmap :: (a -> b) -> f a -> f b As far as I understand ...
5
votes
2answers
433 views

How can a true Vector be implemented in Haskell?

How could a true Vector type be implemented in Haskell? In order for something to be a Vector, it has to be stored sequentially in memory, with O(1) random access. But Haskell hides its memory ...
34
votes
2answers
4k views

Do modern languages still use parser generators?

I was researching about the gcc compiler suite on wikipedia here, when this came up: GCC started out using LALR parsers generated with Bison, but gradually switched to hand-written ...
5
votes
2answers
579 views

Is it safe in Haskell to save a data structure to a file using “show”, and retrieve it using “read”?

Say I have the following types: type EndsTup = (Int,Int) -- (0-based index from start or end, Frequency) type FreqTup = (Char, [EndsTup], [EndsTup]) -- (Character, Freqs from start, Freqs ...
2
votes
2answers
644 views

Is Haskell appropriate for Signal Processing, Communication Systems and Information Theory? [closed]

I have been working on Software-Defined Radio projects for almost a year. This is an area which requires lots of signal processing (digital filters and FFTs), communication theory (modulation, ...
2
votes
4answers
121 views

What's the proper way of dealing with a global file path?

I don't have compilable code, because the code in question depends on a large function that's irrelevant to the question, but say I have the following scenario: savePath = "C:\\..." changePath1, ...
1
vote
2answers
664 views

How bad is using underscore in names? [closed]

I am mainly a C programmer. In my world, writing likeThis or like_this is just a matter of style. In Haskell however, it seems that camelCase is the definite choice. Personally, I find the later much ...
5
votes
1answer
422 views

Why does Haskell's built in max function run faster than mine?

I noticed that for some reason, Haskell's built in max function (which returns the greatest of two numbers) runs much faster than the one I wrote, even though they are essentially identical. From ...
6
votes
1answer
371 views

Who invented Haskell's type classes?

Haskell's type classes are a very powerful tool and give Haskell a great expressive ability, compared to functional languages that don't have them. When were they invented, and who invented them?
7
votes
1answer
383 views

Relation between objects

For a few weeks I’ve been thinking about relation between objects – not especially OOP’s objects. For instance in C++, we’re used to representing that by layering pointers or container of pointers in ...
4
votes
1answer
638 views

Why are data constructors with the same name disallowed in different type constructors?

The following declaration gives an error: type Vec2d = (Float, Float) type Vec3d = (Float, Float, Float) -- Rect x y defines a rectangle spanning from (0,0) to (x,y) data Obj2d = Rect Float Float ...
1
vote
3answers
280 views

Are functional languages a kind of program derivation?

Program derivation is defined as the derivation of a program from it's specifications. Usually this specification language is some form of propositional logic, but from what I understand, it need not ...
9
votes
1answer
2k views

I feel something uncomfortable with Haskell record syntax

Most of Haskell syntax has beauty of purity. But the record syntax looks ugly. It's uncomfortable. It feels some kind of mixture with C. It requires comma and braces. Haskell has tab,line based ...
5
votes
1answer
852 views

Is there an imperative language with a Haskell-like type system? [closed]

I've tried to learn Haskell a few times over the last few years, and, maybe because I know mainly scripting languages, the functional-ness of it has always bothered me (monads seem like a huge mess ...
31
votes
2answers
2k views

Why did the Haskell committee choose monads to represent I/O?

The Clean language uses uniqueness types to handle I/O in a purely functional setting. Why did the Haskell committee go with monads instead? Were there other proposals for handling state that the ...
2
votes
2answers
322 views

Why isn't Haskell able to optimize infinite lists?

Lets say you've got a list l = [0, 2..] and you want to get the nth number when n is pretty large, say n=123456789. So you call l !! 123456789. On my machine, this results in out of memory. So why ...
23
votes
2answers
4k views

Why does Haskell have built-in “if/then/else” instead of defining it as a simple library function?

Why does Haskell have a built-in if/then/else, which is dependent on the Bool type, instead of having a simple library function? Such as if :: Bool -> a -> a -> a if True x _ = x if False _ ...
6
votes
2answers
159 views

Guidelines for returning collections from public functions

The Problem Imagine you have a function in a public API that needs to return some kind of collection. Its type is something like foo :: a -> b where b is some kind of collection. As far as I ...
2
votes
1answer
169 views

To which level Haskell's HDBC is lazy?

The HDBC documentation states: fetchAllRows :: Statement -> IO [[SqlValue]]Source Lazily fetch all rows from an executed Statement. You can think of this as hGetContents applied to a ...
1
vote
1answer
337 views

Picking a card from a shuffled deck

I'm pretty new to Haskell although I did some ML many moons ago. I'm trying to set up a deck of playing cards, shuffle them and then deal them. I have the deck and shuffle sorted (of a fashion) but ...
1
vote
1answer
250 views

What is this programming style? “Monoid-ic”?

In a moderately old blog post, Conal Elliot makes an interesting (if less than serious) argument that C is a purely functional language, by drawing a parallel between the combination of the C ...
17
votes
4answers
2k views

How does persistence fit into a purely functional language?

How does the pattern of using command handlers to deal with persistence fit into a purely functional language, where we want to make IO-related code as thin as possible? When implementing ...
1
vote
2answers
738 views

Why does a monad use “return” or “unit” rather than “lift”?

This is partly genuine curiosity, and partly a check on my understanding. I'm probably missing the point. In Haskell, why does a monad use operations called return or unit to describe putting a type ...
15
votes
6answers
719 views

Introducing functional programming into your development environment [closed]

This is a long story but I will try to summarize it as best I can. We are a .NET shop that writes software for a variety of different types of funds. For example, we write health claims management ...
36
votes
2answers
5k views

Misconceptions about purely functional languages?

I often encounter the following statements / arguments: Pure functional programming languages do not allow side effects (and are therefore of little use in practice because any useful program does ...
2
votes
2answers
644 views

Mapping a list of optional values to an optional list of values

I have encountered the following pattern while programming in Haskell (but the pattern could occur in any language supporting lists, option types, and mapping of a function over a list). I have types ...
27
votes
3answers
3k views

Different ways to see a monad

While learning Haskell I have faced a lot of tutorials trying to explain what are monads and why monads are important in Haskell. Each of them used analogies so it would be easier to catch the ...
4
votes
2answers
490 views

Is there any particular reason for the use of lists over queues in functional programming languages?

Most functional programming languages such as Scheme and Haskell use lists as their main data structure. Queues are identical to lists, except for the fact appending to the end - not to the begin - ...
2
votes
1answer
202 views

Building proprietary software over haskell compiler [closed]

Is it perfectly legal to use GHC as base and build some commercial application over its top ? Are there such examples I can can interact with ?
9
votes
2answers
1k views

Can someone explain the concept behind Haskell's memoization?

(note I'm putting the question here because it's about the conceptual mechanics of it, rather than a coding problem) I was working on a small program, that was using a sequence of fibonacci numbers ...
13
votes
2answers
608 views

Are types erased in Haskell?

Haskell has a notion of “generic functions” that has some apparent similarity with common lisp—having neither experience with Haskell nor with common lisp, I might be very approximative here. This ...
16
votes
2answers
446 views

Side effect-free interface on top of a stateful library

In an interview with John Hughes where he talks about Erlang and Haskell, he has the following to say about using stateful libraries in Erlang: If I want to use a stateful library, I usually build ...
1
vote
1answer
366 views

Haskell: Best tools to validate textual input?

In Haskell, there are a few different options to "parsing text". I know of Alex & Happy, Parsec and Attoparsec. Probably some others. I'd like to put together a library where the user can input ...
19
votes
2answers
2k views

Type checking and recursive types (Writing the Y combinator in Haskell/Ocaml)

When explaining the Y combinator in the context of Haskell, it's usually noted that the straight-forward implementation won't type-check in Haskell because of its recursive type. For example, from ...
11
votes
2answers
1k views

Functional programming and stateful algorithms

I'm learning functional programming with Haskell. In the meantime I'm studying Automata theory and as the two seem to fit well together I'm writing a small library to play with automata. Here's the ...
8
votes
1answer
950 views

Maths needed to understand theory behind Haskell's type system?

Recently, I've become deeply interested in Haskell. While attempting to learn new concepts (e.g. the forall keyword and ST monad) and Haskell's type system in general, I continually run into ...
37
votes
4answers
12k views

Are there any downsides or problems with Haskell?

I'm looking at diving into Haskell for my next (relatively trivial) personal project. The reasons that I'm tackling Haskell are: Get my head into a purely functional language Speed. While I'm sure ...
24
votes
3answers
13k views

What are the advantages of using LISP and Haskell? Will they make me a better programmer? [closed]

I know Lisp and Haskell are functional and logic programming languages respectively, but what exactly does this mean? How do they differ from other languages? I've heard that learning these will make ...
1
vote
2answers
992 views

Why don't we have a non-turing complete general purpose language yet? [duplicate]

Non-turing complete languages can solve every practical problem that a turing-complete language can. Also, they are much more analyzable than turing complete languages. The compiler can comprehend the ...
11
votes
2answers
2k views

Haskell memory efficiency - which is the better approach?

We are implementing a matrix compression library based on a modified two dimensional grammar syntax. Now we have two approaches for our data types -which one will be better in case of memory usage? ...
8
votes
2answers
443 views

Choosing the language to build an app in based on hiring market vs performance and maintainability [closed]

I'm facing a choice of whether to start building Haskell components for a certain production app that is all done in Ruby. I'm leaning toward Haskell for several reasons, primarily speed (compiled ...
8
votes
3answers
668 views

When is it a good time to reason about performance in Haskell?

Simon Peyton Jones himself recognizes that reasoning about performance in Haskell is hard due to the non strict semantics. I have yet to write a significant project in haskell so I wonder: can I ...
8
votes
2answers
556 views

Is Haskell function composition an instance of pipe & filter architectural pattern

The pipe & filter architectural pattern is defined as a chain of processing elements, arranged so that the output of each element is the input of the next. Every example seems to consider ...
2
votes
5answers
787 views

The rationale behind Falsy values [closed]

I'm wondering what the arguments for/against Falsy values are. On what principles would you decide to add or exclude them from a language? Are there any problems you could see them causing off-hand? ...
12
votes
2answers
981 views

Functional reactive programming — is Fay expressive enough?

So I'm doing a fairly involved javascript/html client with lots of ajax calls and other involvements of callback-ism. I'm entertaining the thought of using Fay for this purpose. I'm aware of Elm. ...
8
votes
2answers
2k views

Could we build a functional computer?

As mush as FP has done, in the end, all our programs are structured. That is, it doesn't matter how pure or functional we make a them - they are always translated to assembly, so what actually runs ...