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Silly job interview questions in Haskell
- pensatoio 1y agoFifteen years into my career, and I'm finally realizing that "expressive" languages are practically unreadable.
- tikhonj 1y agounfamiliar languages are practically unreadable
- rhdjsjebshjffn 1y agoI don't see how that's any better for a haskell shop. i got some empathy but you chose a rough life.
- yakshaving_jgt 1y agoThe trick is to hire people who are familiar with the language.
- rhdjsjebshjffn 1y ago[flagged]
- sponnath 1y agoNot all programming languages are obvious derivatives of C. Haskell is pretty readable once you spend some time getting to know the syntax.
- 90s_dev 1y agoThe semantics are very different. It's much closer to a mathematical proof than a C program with different syntax, in terms of its lazy evaluation.
- Darmani 1y agoI prefer to think of Haskell-like lazy evaluation as constructing a dataflow graph. The expression `map f (sort xs)` constructs a dataflow graph that streams each output of the sort function to `f`, and then printing the result begins running that job. Through that lens, the Haskell program is more like constructing a Spark pipeline. But you can also think of it as just sorting a list then transforming each element with a function. It only makes a difference in resource costs or when there's potential nontermination involved, unless you use unsafe effects (e.g.: unsafePerformIO). Is there a way to think of proofs as being lazy? Yes, but it's not what you think. It's an idea in proof theory called polarization. Some parts of a proof can be called positive or negative. Positive parts roughly correspond to strict, and negative roughly correspond to lazy. To explain a bit more: Suppose you want to prove all chess games terminate. You start by proving "There is no move in chess that increases the number of pieces on the board." This is a lemma with type `forall m: ChessMove, forall b: BoardState, numPieces b >= numPieces (applyMove m b)`. Suppose you now want to prove that, throughout a game of chess, the amount of material is decreasing. You would do this by inducting over the first lemma, which is essentially the same as using it in a recursive function that takes in a board state and a series of moves, and outputs a proof that the final state does not have more material than the initial state. This is compact, but intrinsically computational. But now you can imagine unrolling that recursive function and getting a different proof that the amount of material is always decreasing: simply write out every possible chess game and check. This is called "cut elimination." So you can see there's a sense in which every component of a proof is "executable," and you can see whether it executes in a strict or lazy manner. Implications ("If A, then B") are lazy. Conjuctions ("A and B") can be either strict or lazy, depending on how they're used. I'm at the edge of my depth here and can't explain more -- in honesty, I never truly grokked proof polarization. Conversely, in programming languages, it's not strictly accurate to say that the C program is strict and the Haskell program is lazy. In C, function definitions and macro expansions are lazy. You can have the BAR() macro create a #error, and yet FOO(BAR()) need not create a compile error. In Haskell, bang patterns, primitives like Int#, and the `seq` operator are all strict. So it's not the case that proofs are lazy and C is strict and Haskell is lazy so it's more like a proof. It's not even accurate to say that C is strict and Haskell is lazy. Within a proof, and within a C and a Haskell program, you can find lazy parts and strict parts.
- rrradical 1y agoAs a haskell programmer, all of that was easily readable.
- sgarland 1y agoAs a non-Haskell programmer, all of that was easily readable. Straightforward words for functions makes that pretty easy.
- RHSeeger 1y agoThere were a couple of places that took me a couple reads to figure out, like the fact that `(x:)` was "prepend". But overall, I followed the code pretty well. From the context of someone that wrote a small amount of Haskell a decade ago.
- StopDisinfo910 1y agoIt’s partial application of cons via the operator, admittedly a poor choice from Haskell, a language which likes operators a bit too much. I think eta-expansion makes the whole thing clearer: (\xs -> x:xs) but most Haskellers would disagree. The article also features examples of point-free style, another unfortunate trend for readability. As long as you use operators sparingly, don’t abuse partial application and prefer explicit lambdas to composition, Haskell is fairly readable. The issue is that approximately no Haskeller writes Haskell this way.
- deleted 1y ago[deleted]
- Skeime 1y agoI don't use Haskell nearly enough to call myself a Haskeller but I will still disagree. Yes, operator sections are yet another thing to learn but I find them very intuitive, and actually easier to read than the equivalent lambda expression because I don't have to match up the bound variable. (For example, (\x -> x ++ y) and (\y -> x ++ y) look pretty similar to me at first glance, but (++y) and (x++) are immediately distinguishable.) Of course, this is reliant on knowing the operators but that seems like a mostly orthogonal issue to me: You still need to know the operator in the lambda expression. That said, the niceness of sections gives people yet another reason to introduce operators for their stuff when arguably they already are too prevalent.
- bcrosby95 1y agoHow much time have you spent with functional programming languages?
- djtango 1y agoWe once hired a F# developer to write Clojure and within a week, he was writing some of the clearest Clojure I've read. Learn paradigms not languages...
- rhdjsjebshjffn 1y ago[flagged]
- 90s_dev 1y agoFor one thing, it's hard to know what to spend it on. What should take priority? Obviously your own basic needs, for starters. And then of course the needs of your immediate dependents. But then what? Do you try to increase your quality of life? Theirs? At what point do you draw the line and begin to help others altruistically? Are two coins worth more than billions in practice? Besides, what even is quality of life? It's a very difficult and heavy problem. One I'm glad I don't have.
- zwnow 1y agoAltruism? In rich folk? Usually they convince themselves on thinking they need stuff they don't actually need. Employees can't afford everyday life? Not their issue.
- fkfyshroglk 1y ago> it's hard to know what to spend it on. Probably not Haskell developers, but then again, I don't have enough money for my opinions to be worth anything. > One I'm glad I don't have. you should probably put less thought into it if you want to be happy & not grapple with such difficult thoughts. > At what point do you draw the line and begin to help others altruistically? At the point you have money, IMO. Otherwise what is the point of having money?
- deleted 1y ago[deleted]
- Sourabhsss1 1y agoWords for the functions are easy to understand.
- lynx97 1y agoWell, that fizlle implementation is not a good example of a great answer. It checks for the two conditions twice. At least I would use a where clause to define fizz and buzz.
- internet_points 1y agowhich is nice with the laziness because you only eval what you need, e.g. fizzle :: Int -> String fizzle n | fizz && baz = "Fizz Baz!" -- if this branch is taken, buzz is never evaluated | fizz && buzz = "Fizz Buzz!" | fizz = "Fizz!" | buzz = "Buzz!" | otherwise = show n where fizz = n `mod` 3 == 0 buzz = n `mod` 5 == 0 baz = n `mod` 7 == 0
- throwaway81523 1y agoThat doesn't handle all the cases: what about fizz buzz bazz? Added: here's my version, which maybe could be cleaned up further. The spaces and exclamation point make the problem trickier. {-# LANGUAGE MonadComprehensions #-} import Data.Maybe (catMaybes) import Data.List (intercalate) fizz :: Int -> String fizz n = case zub of [] -> show n otherwise -> intercalate " " zub ++ "!" where f :: Int -> String -> Maybe String f d msg = [msg | n`rem`d == 0] zub = catMaybes . map (uncurry f) $ [(3,"Fizz"), (5,"Buzz"), (7, "Bazz")] main = mapM_ putStrLn [fizz n | n <- [1..110]]
- throwaway81523 1y agoimport Data.List (intercalate) fizzle :: Int -> String fizzle n = let ws = [(3,"Fizz"), (5,"Buzz"), (7,"Bazz")] a = [s | (d,s) <- ws, n`rem`d == 0] in case a of [] -> show n otherwise -> intercalate " " a ++ "!" main = mapM_ (putStrLn . fizzle) [1..110]
- djtango 1y agoI remember I did an Advent of Code day 1 in Haskell a while back. The meat of the code was a one liner. But opening a file, throwing away the first line and parsing a CSV took a lot more head scratching, especially if you've only ever done puzzles in Haskell. Makes the hard things easy and the easy things hard
- ngruhn 1y agoSame. Until I discovered those parser combinator libraries which are THE way to do parsing in Haskell. It makes parsing so pleasant you'll never need a regex again. A parser for that CSV file probably looks like this: line = decimal `sepBy` char ',' file = line `sepBy` newline That's it. It almost reads like prose.
- djtango 1y agoThanks for sharing! This was in a pre-LLM era and I couldn't be bothered to research the right way to do this. Those parser combinators are excellent, so clean
- rafram 1y agoThat wouldn’t be a very good CSV parser.
- Tainnor 1y agoIt doesn't have to be a general purpose CSV parser, it just has to be able to parse the specific AoC input
- nh23423fefe 1y ago<input runhaskell -e 'interact (oneliner . parse . drop 1 . lines)'
- sshine 1y agoI live-coded Haskell a couple of times at job interviews for non-Haskell positions where you were free to choose. It’s fun because the interviewer often doesn’t grok the paradigm. In one case, I was asked to make a password generator, and I went with QuickCheck’s Gen, which lets me write a random generator of things without explicitly defining a single function (they’re all monads). So you go from somehow describing the thing you want to make to “I’m done.” :-D
- 18172828286177 1y agoDid you get the job?
- sshine 1y agoYeah. I also refused to solve a part of the task because it would lead to bad password policy. Instead I property-tested the generator.
- thdhhghgbhy 1y agoTypical Haskell coding post with no mention of order or efficiency of the algorithm solutions. The thing is, even in basic coding quizes, if the interviewer is worth their salt, they will ask about how to improve the efficiency of the naive solutions first put forward, like the palindrome answer in this post. What is the order of sumNToTotal?
- Paracompact 1y agoThe execution order, or the order of the output list? The latter should be self-evident from the function body (first elements get collected first), and the former holds no tricks either since filters are evaluated from the head first, and concat (<>) allows lazy access to the first list's elements. This is just a beginner's Haskell post. If an interviewer really meant to test optimization knowledge, I would hope they wouldn't ask me to optimize one O(n) utility function into another.
- dmurray 1y agoIt does discuss performance and points out some places where the Haskell implementation makes the natural naive solutions performant. > While it's true that sort has an O(nlogn) performance profile, one interesting thing here is that sorting is lazy in Haskell! This means that if our two strings are unequal, they will only be sorted far enough to determine inequality! I don't understand exactly how this works - don't all O(n log n) sorting algorithms still have to do some work on the other elements of the list before pulling out the smallest one? If you just scanned and pulled the smallest one to the front each time that is O(n^2). And there's an implementation detail here that differences at the start of the sorted string will be caught more quickly than at the end, so real-world behaviour is dependent on your choice of sort order. Agreed that the performance analysis is quite superficial and that some of the solutions like sum NToTotal must be very sub-optimal.
- deleted 1y ago[deleted]
- iamevn 1y agowith N as the length of the subsets and X as the length of input, `combinations n xs` basically walks through list xs and at each element, conses that element onto each combination of size n-1 of later elements in the list then appends those resulting lists together. this is on the order of N * nCr(X, N) aka O(NX!/(N!(X-N)!)) which dominates the overall runtime. the final filter walks through each combination and does O(N) work at each element to find the ones that sum to the desired amount, again O(NX!/(N!(X-N)!))
- pentaphobe 1y agoAlways fun to see this kind of Rosetta Code thing, feel like no matter the topic there's something to glean from reading! That said: if I ever gave the palindrome question to a candidate (I haven't) and they pulled out a `reverse` library func/keyword we'd be encouraging them to do more.
- chriswarbo 1y agoHaskell's default `String` type is a singly-linked list of `Char` values[0] so it takes O(n) time to access the end of the string. Hence I think the solution using `reverse` is probably the best there is, since any attempt to be "smarter" would just be more complicated for no real performance gain. Though I agree that we could ask someone to also write their own reverse function. [0] https://hackage.haskell.org/package/base-4.21.0.0/docs/Prelude.html#t:String https://hackage.haskell.org/package/base-4.21.0.0/docs/Prelu...
- pentaphobe 1y ago"... write their own reverse.." Yeah spot on - exactly what I was aiming at too... Having the intuition to use reverse (& pragmatism to keep it simple) is a great sign, and realistically more valuable [to me] for hiring than implementing rudimentary algorithms, but... still want at least a bit of both abilities Also knowledge of standard library / language features is useful but (for me) doesn't equate to abilities in complex problem solving. But honestly could be bias :)
- kevincox 1y agoI generally say something like "You can use whatever libraries you like but I reserve the right to ask you to implement them yourselves". This allows them to focus on the part they want to focus on and shows good decision making about not re-inventing the wheel, but if they "outsource" the core of the problem (or we just have extra time) there is an obvious step deeper that can be taken. I usually even say that they can make up library APIs if they want, because I don't really care if they have memorized the python stdlib, I just want to seem them think about and work on a coding problem.
- ReDress 1y ago> Silly job interview questions in Haskell. Well, it's not clear to me why we're terming these as silly. They mostly seem simple, instead, to me.