A functional programming language

learn more… | top users | synonyms

5
votes
2answers
85 views

Dealing with (the risks of) infinite sequences in Haskell

I'm a couple of weeks into dabbling with haskell and I've made a pretty big dent in Learn You A Haskell. I feel like many of the type classes and common implementations up to applicatives and monads ...
2
votes
0answers
51 views

Event driven programming in Haskell

I'm new to Haskell, so this is more a high-level conceptual question. I've read this: https://wiki.haskell.org/Real_World_Applications/Event_Driven_Applications and it has this: run :: Domain -> ...
3
votes
2answers
146 views

Can a function be polymorphic and overloaded?

In Graham Hutton's book "Programming in Haskell", he defines a function to be polymorphic, if its type "contains one or more type variables". He then defines a function to be overloaded, if its type ...
19
votes
1answer
1k views

Could Hindley-Milner inference work for the Go language?

I've read that Hindley-Milner does not work with type systems that have subclasses, and there are other type system features that also do not work well with it. Go currently has only very limited type ...
5
votes
2answers
141 views

Why isn't Bounded a subclass of Enum in Haskell

It seems like any Bounded instance should have a sane implementation of Enum. I cannot personally think of a counterexample, although if someone comes up with one that isn't pathological then I will ...
8
votes
2answers
1k views

Implement Haskell typeclass with C# interface

I'm trying to compare Haskell's type classes and C#'s interfaces. Suppose there is a Functor. Haskell: class Functor f where fmap :: (a -> b) -> f a -> f b How to implement this type ...
0
votes
1answer
232 views

Why does this article state that graduate education liberate one from concerns like the efficiency of hardware-based integers? [closed]

Quoting The Evolution of Haskell Programmer, graduate education tends to liberate one from petty concerns about, e.g., the efficiency of hardware-based integers What exactly does this ...
2
votes
1answer
77 views

Difference between Python classes and Haskell typeclasses

I'm an intermediate Python dev and just starting out with Haskell. It seems like Python's classes can be used in a way that is similar to how Haskell's typeclasses are used. It seems like typeclasses ...
7
votes
6answers
2k views

A programming language that does not allow IO. Haskell is not a pure language

Are there any 100% pure languages (as I describe in the Stack Overflow post) out there already and if so, could they feasibly be used to actually do stuff? i.e. do they have an implementation? I'm not ...
36
votes
7answers
15k views

Haskell AND Lisp vs. Haskell OR Lisp [closed]

I currently code with C, C++, and Python. I'm wanting to pick up a functional programming language, and right now I'm leaning toward Haskell. I do NOT want to start a "Haskell vs Lisp" war here; what ...
64
votes
5answers
9k views

Is Haskell's type system formally equivalent to Java's? [closed]

I realize some things are easier/harder in one language than the other, but I'm only interested in type-related features that are possible in one and impossible/irrelevant in the other. To make it ...
5
votes
3answers
190 views

Should databases be viewed as Monads?

Because any kind of persistence updates/inserts/deletes represents in some sense a kind of state change in a database, it makes me wonder whether databases can be considered monads. We say the same ...
3
votes
1answer
89 views

Can I use maybe on multiple inputs in Haskell?

Suppose I wanted to test that both my inputs are positive. Can I do something like this? test :: Float -> Float -> Maybe Float Float test a b | a>0 && b>0 = a b | ...
23
votes
8answers
3k views

Using a “strong” type system in the real world, say, for large-scale web-apps?

I know this is a very broad, ambiguous, and possibly philosophical question. To an extent, that the most important keyword in the question - "strong" type system - itself, is ill-defined. So, let me ...
3
votes
3answers
110 views

Iterating (mapping) recursive data type in Haskell

This might me a stupid question, but since I don't have anyone to discuss it over a coffee, I think I'd ask it here. So, I'm reading the book "The Haskell School of Expression" to learn myself a bit ...
40
votes
2answers
4k views

Why (or why not) are existential types considered bad practice in functional programming?

What are some techniques I might use to consistently refactor code removing the reliance on existential types? Typically these are used to disqualify undesired constructions of your type as well as to ...
4
votes
3answers
203 views

How to use a strong type system to model business constraints?

Following up on my ambiguous question, here's a question that is probably more focused. Consider the following code snippet form a Haskell program: data NightWatchCommand = InvalidCommand | ...
10
votes
2answers
286 views

Haskell ways to the 3n+1 problem

Here is a simple programming problem from SPOJ: http://www.spoj.com/problems/PROBTRES/. Basically, you are asked to output the biggest Collatz cycle for numbers between i and j. (Collatz cycle of a ...
18
votes
2answers
864 views

Is it possible to “bake dimension into a type” in haskell?

Suppose I want to write a library that deals with vectors and matrices. Is it possible to bake the dimensions into the types, so that operations of incompatible dimensions generate an error at compile ...
3
votes
6answers
2k views

How can IO cause side effects in Functional Programming? [duplicate]

Whenever I read about Haskell, I find that IO can cause side effects. But I do not understand how it would do it? Do we mean that we are writing to a file from one lazy sequence and another lazy ...
4
votes
2answers
491 views

Why do textbooks use pseudocode rather than real languages?

In colleges and in algorithm textbooks, it is quite common for the teacher and author to explain control flow in pseudo-code. With the advent of more expressive languages like Python and Haskell among ...
7
votes
1answer
223 views

Computer Architectures NOT based on arrays [closed]

Wadler's original paper on Monads for Functional Programming ( Haskell ) ,he says Another question with a long history is whether it is desirable to base programs on array update. Since so much ...
4
votes
3answers
3k views

Lambda expressions with no parameters in Haskell and / or lambda calculus

In eager languages like Scheme and Python, you can use a lambda expression without parameters to delay evaluation, e.g. in Scheme (Chicken Scheme): #;1> (define (make-thunk x) (lambda () (+ x 1))) ...
2
votes
2answers
145 views

What is the equivalent of The Little Lisper project in Haskell?

In the book The Little Lisper, you implement a minimal Scheme in 10 Chapters that is capable of interpreting any chapter in the book. To me it seems you could do the same for a 'minimal subset of a ...
1
vote
0answers
60 views

Chronological/evolutionary positioning of Curry in relation to Haskell and Prolog

is Curry a transitional language from FP to Logic Programming (Haskell to Prolog), like Scala is a transitional language from imperative to FP (Java to Haskell)? I find it hard to come up with a ...
22
votes
4answers
3k views

Is return-type-(only)-polymorphism in Haskell a good thing?

One thing that I've never quite come to terms with in Haskell is how you can have polymorphic constants and functions whose return type cannot be determined by their input type, like class Foo a ...
1
vote
2answers
198 views

Functional Programming style: How to write functions - explicit currying, implicit currying or lamdas?

So I have been using F# for a while and studying a bit of Haskell on the side and I have realized I could rewrite the exact same function one of three different ways. Either with implicit currying, ...
2
votes
2answers
182 views

Haskell types for functions

I don't understand the answer to this question: Q: Can Haskell find a type for the function selfapply defined by: selfapply f = f f A: The function selfapply is not typeable in the simple ...
8
votes
4answers
354 views

Is there a Haskell idiom for trying several functions and stop as soon as one succeeds?

In Haskell, I can use the type a -> Maybe b to model a function that either returns a value of type b, or returns nothing (it fails). If I have types a1, ..., a(n+1) and functions f1, ..., fn, ...
7
votes
6answers
1k views

Does it make sense to use the term “Space Leak” with regard to Java?

EDIT: To clarify, I am not suggesting that leaks don't happen in a managed application. I'm simply pondering about how we talk about them. There are some highly upvoted discussions about memory ...
35
votes
5answers
2k views

“A proof is a program; the formula it proves is a type for the program”

This might be a philosophical kind of question, but I believe that there is an objective answer to it. If you read the wikipedia article about Haskell, you can find the following: The language is ...
5
votes
4answers
622 views

How does “repeat x = x:repeat x” return a list in Haskell?

This is supposed to return an infinite list of x's. However a list is created using an element, then the operator ':' and then a list. The recursive definition of repeat' x = x:repeat' x seems to ...
3
votes
2answers
168 views

Haskell: Is it possible to convert a Num to a Float?

I need to be able to convert generic numbers (instances of Num) to a Float. I searched Hoogle for a function with the signature Num n => n -> Float, but I couldn't find any such functions ...
6
votes
3answers
198 views

What is the purpose of wrapped values in Haskell?

I've recently read an article about Functors, Applicatives and Monads in Haskell and it concludes with these statements: functors: you apply a function to a wrapped value using fmap or <$> ...
127
votes
5answers
24k views

What exactly makes the Haskell type system so revered (vs say, Java)?

I'm starting to learn Haskell. I'm very new to it, and I am just reading through a couple of the online books to get my head around its basic constructs. One of the 'memes' that people familiar with ...
82
votes
13answers
49k views

Is Haskell worth learning? [closed]

I am looking at this question primarily from a career point of view, so I hope you answer it accordingly. I am fairly proficient with Python, can write C++ and I am a final year student of computer ...
64
votes
2answers
11k views

What is the “Free Monad + Interpreter” pattern?

I've seen people talking about Free Monad with Interpreter, particularly in the context of data-access. What is this pattern? When might I want to use it? How does it work, and how would I implement ...
41
votes
7answers
6k views

How do you encode Algebraic Data Types in a C#- or Java-like language?

There are some problems which are easily solved by Algebraic Data Types, for example a List type can be very succinctly expressed as: data ConsList a = Empty | ConsCell a (ConsList a) consmap f ...
4
votes
2answers
355 views

Is there any practical use for the empty type in Common Lisp?

The Common Lisp spec states that nil is the name of the empty type, but I've never found any situation in Common Lisp where I felt like the empty type was useful/necessary. Is it there just for ...
5
votes
3answers
2k views

What is this algorithm for converting strings into numbers called?

I've been doing some work in Parsec recently, and for my toy language I wanted multi-based fractional numbers to be expressible. After digging around in Parsec's source a bit, I found their ...
9
votes
2answers
532 views

Maintaining State without assignment

I am learning functional programming and I have trouble understanding how some particular scenarios are implemented without the use of assignment. The following simple problem pretty much sums up my ...
6
votes
3answers
196 views

Why don't “multi-infinite” list comprehensions work with lazy evaluation?

As a simple demonstration of the efficiency of Haskell style, I thoughtlessly ran the following: take 100 [(a, b, c) | a <- [1..], b <- [1..], c <- [1..], a^2 + b^2 == c^2] This should be a ...
9
votes
2answers
2k views

Why is the Scala Option type not called Maybe, just as in Haskell? [closed]

Why is the Scala Option type not called Maybe, just as in Haskell? Maybe makes a lot more "semantic sense" to me, but maybe Option has different behaviour I am not aware of. Is there any particular ...
4
votes
1answer
74 views

Performance of list concatenation followed by scanning

Consider the following code snippet: -- list_1 = [1, 2, 3] -- list_2 = [4, 5, 6] final_list = list_1 ++ list_2 result = map (+1) final_list Is the time spent by it proportional just to the length ...
23
votes
3answers
13k views

Haskell vs Erlang for web services

I am looking to start an experimental project using a functional language and am trying to decide beween Erlang and Haskell, and both have some points that I really like. I like Haskell's strong ...
16
votes
1answer
476 views

Haskell build and artifact environment similar to Maven

I used to be a Java developer for a long time, but recently, I joined a Haskell team. In the java world, if you have a large project, with several teams working on it, a common approach is to use an ...
3
votes
1answer
232 views

How to manage the state in a GUI app with Haskell

I am using wxHaskell to create a simple GUI that has typical components like Buttons, Panels, etc. When some of these components perform an action (like callback), the generic status of the ...
0
votes
1answer
101 views

The use of '#'-sign in haskell program text

What do those #-signs mean? For example, data Word = W# Word# deriving (Eq, Ord) I tried to google it but I found nothing.
0
votes
0answers
104 views

Haskell + OpenGL framework

I'm writing a framework in Haskell where I'd like to use OpenGL to draw lines, shapes... I'm encountering a problem defining the structure of my program. I have for example a Polyline type which holds ...
1
vote
1answer
82 views

how do interpreters differ for statically- or dynamically-typed languages?

Writing an interpreter for a dynamically typed language usually involves creating an Environment, a data structure which stores mappings of variable names to their values. Values are boxed in some ...