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Why I never finish my Haskell programs

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Re: Why I never finish my Haskell programs

#151

Post by thomasjm42 »

I think the problem in this case is that the author's attempt at generalization went off in the wrong direction.

The fact that fixed-length lists aren't working well as a representation for polynomials is a hint. Polynomials with real coefficients form a vector space [0], so you should really think of them as infinite-dimensional lists of numbers (in which most of the numbers are zero).

Once you know you want to represent an infinite dimensional vector with only a few nonzero entries, you can use a sparse vector. The first library that comes up when you google "Haskell sparse vector" is `Math.LinearAlgebra.Sparse.Vector`, which lets you write something like this (I haven't run this code but it should get the job done):

import Math.LinearAlgebra.Sparse.Vector as V

poly1 = V.sparseList [1, -3, 0, 1]

poly2 = V.sparseList [3, 3]

sumPolys = V.unionVecsWith (+)

So, I read this more as an article about trying to reinvent the wheel in a domain which isn't necessarily simple, which isn't a good idea in any language.

[0]: https://en.wikipedia.org/wiki/Examples_of_vector_spaces#Poly...

Re: Why I never finish my Haskell programs

#152

Post by desdiv »

jlebar wrote: post #106

I am not a Haskell programmer, but is this correct? (Poly a) + (Poly b) = Poly $ addup a b where addup [] b = b addup a [] = a addup (a:as) (b:bs) = (a+b):(addup as bs) Imagine a simple example, adding `x+2` and `10`. In OP's representation, these would be represented as the lists [1, 2] and [10]. That is, the first element is the coefficient of the term of highest degree. But doesn't this implementation add list ele…

You're misreading OP's representation:

> The polynomial x^3 −3x +1 is represented as Poly [1, -3, 0, 1]

It starts with the 0th coefficient and goes up. So adding `x+2` and `10` would be zip-adding lists [2,1] and [10,0].

Re: Why I never finish my Haskell programs

#153

Post by rzzzt »

abecedarius wrote: post #36
rzzzt wrote: post #13

Earlier quoted context omitted.

Evaluation also becomes easy this way, using Horner's method: https://en.wikipedia.org/wiki/Horner%27s_method#Python_imple...

But this doesn't argue for the low-to-high order, because of reversed(). This code would be simpler and faster with the coefficients in the opposite order.

You're right, the process does start from the higher coefficients, and so does not really support the ordering presented.

You either need to use foldr to defer the multiply-and-add until the end of the list is processed, or reverse the list before processing it.

Re: Why I never finish my Haskell programs

#154

Post by anonytrary »

chongli wrote: post #108
hhmc wrote: post #27

I'm reminded of one of my favourite HN comments on Haskell: 'There's something very seductive about languages like Rust or Scala or Haskell or even C++. These languages whisper in our ears "you are brilliant and here's a blank canvas where you can design the most perfect abstraction the world has ever seen.' https://news.ycombinator.com/item?id=7962612 Although it's not 100% applicable in this case (unless you argue…

The blank canvas analogy is a good one but for the wrong reason. Think of the aspiring novelist with a blank stack of paper in front of them. The problem is not the freedom they have, it's their lack of discipline. It's far easier to write PR for an agency or injury reports for a sports blog than it is to write a novel. The reason so many programmers struggle with this problem is because nobody is paying them to writ…

> People only go down rabbit holes when they don't have a manager breathing down their neck all day.

I've experienced this first hand. If I can't find a basket of Easter eggs within the 30 minutes of my journey into a rabbit hole, I have to backtrack and move on to something else. I do not feel this limitation when I'm at home, doing things on my own volition.

Re: Why I never finish my Haskell programs

#155

Post by anonytrary »

taeric wrote: post #147
chongli wrote: post #108

Earlier quoted context omitted.

The blank canvas analogy is a good one but for the wrong reason. Think of the aspiring novelist with a blank stack of paper in front of them. The problem is not the freedom they have, it's their lack of discipline. It's far easier to write PR for an agency or injury reports for a sports blog than it is to write a novel. The reason so many programmers struggle with this problem is because nobody is paying them to writ…

Better than a manager, is a customer. Though, any stakeholder is probably better than none, which I believe is your main point. (And one I agree with.)

I've always found interacting with clients to more satisfying than interacting with a manager. Managers have a probability of feeling like unnecessary middlemen, which presents a conundrum because they are your manager.

Re: Why I never finish my Haskell programs

#156

Post by tincholio »

nextos wrote: post #118
pash wrote: post #49

I think many beginning Haskellers have this problem. To overcome it, my advice is to write Haskell code with the knowledge that you can re-write it more readily than you can re-write code in many other languages. Write the code that fits the immediate application, and rely on the type-checker to make it straightforward to refactor when the need arises. I think that’s what many experienced Haskellers would say is the…

In my case, I think it's because large programs always end up containing subproblems that can be better expressed in other paradigms than functional. And it becomes frustrating when I can't shoehorn them to the Haskell way of doing things. My favorite languages are, for this reason, multi-paradigm: Common Lisp, Mozart/Oz, Scala and C++. It's a bit like building La Sagrada Familia (and that's why it's depicted in the…

I agree with your sentiment, but I find the analogy to La Sagrada Familia funny, in that is has still not been finished, it's a black hole for money, and you can see, clearly, it's a hodge-podge of styles... All characteristics that might not be good for your software project.

Re: Why I never finish my Haskell programs

#157

Post by wbillingsley »

yogthos wrote: post #48
mac01021 wrote: post #28

Earlier quoted context omitted.

I don't disagree in general but is Haskell a big language?

I think the complexity in Haskell largely comes from its advanced type system and laziness. For example, pervasive use of monads in Haskell is a direct result of encoding side effects using the type system. You can't just put a log statement in a function, you have to do a whole design exercise of how to push it to the edge of the application.

This is one of the things I rather like about Scala. It still leaves suitable room for the programmer to decide "that doesn't count", and defer deciding what does / does not count until after they have their application sketched out.

Your "pure" function can become "pure except for logging", "pure except for analytics calls", "pure except for notifications", or whatever you decide.

Re: Why I never finish my Haskell programs

#158

Post by wbillingsley »

gowld wrote: post #100
seanmcdirmid wrote: post #47

Earlier quoted context omitted.

There are some languages that tempt more abstract navel gazing than others. I’m not sure about Haskell, but Scala tends to do that. Anyways, there is something about human behavior and language design that can lead “more is less” situations.

If you don't have a use case creating a need that your program solves, what's the difference between figuring out make a zygohistomorphicanedoreticular for polynomials and writing a working library that no one uses? Either way, you do whatever is fun for you. If you have an actual customer requirement, then that guides your prioritization and attention?

More often, you do have a use case, you just don't quite know what it is yet.

Re: Why I never finish my Haskell programs

#159

Post by hohenheim »

pash wrote: post #49

I think many beginning Haskellers have this problem. To overcome it, my advice is to write Haskell code with the knowledge that you can re-write it more readily than you can re-write code in many other languages. Write the code that fits the immediate application, and rely on the type-checker to make it straightforward to refactor when the need arises. I think that’s what many experienced Haskellers would say is the…

Completely agree with you, and I like to add that this is true for any programming language really. Often I find people, specially juniors, obsessed with how they solve a problem and design patterns used than actually solving a problem. To be honest I was once such a person.

The best advice, as you stated it, is to go with the first instinct, and then refine it, IF needed. It might turn out that the code you wrote was redundant anyway.

Re: Why I never finish my Haskell programs

#160

Post by AlexCoventry »

hota_mazi wrote: post #137
yogthos wrote: post #107

Earlier quoted context omitted.

I find that the Haskell community is very friendly as long as you buy into their approach to solving problems. However, my experience is that if you question the effectiveness of static typing, or ask for evidence in support of the claimed benefits you'll get a very hostile reaction. The comment above where pka snidely claims that using any alternative to types amounts to yolo is quite representative. He outright dis…

Facts have been presented to you multiple times but your adoration of Clojure just makes you dismiss them outright. People who claim dynamic type systems are superior to static ones can be dismissed in much the same way flat earthers can because both choose to dismiss evidence they find inconvenient.

I was going to suggest that yogthos may just be thinking of that one guy who converted from clojure to haskell and had a convert's typical evangelical zeal in #clojure, but then I read your reply. Ironic.
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