A primer on the cruel, tacit laws of type-level programming in Haskell | Hacker News Reader

A primer on the cruel, tacit laws of type-level programming in Haskell

aymannadeem.com

117 pointstenslisi62 comments

Kinds in Haskell seem to be evolving in the direction of controlling the representation of datatypes in memory. * (also called Type) is the kind of types whose values are "lifted": they can be lazy computations which might cause an infinite loop, throw an exception, and so on.

There are also kinds for types whose values are "unlifted", meaning they really correspond to actual values in memory, not lazy thunks.

Right now the language for expressing unlifted datatypes is quite limited. Hopefully it will be expanded so that we can write "strict Haskell" more easily.

"Levity polymorphism" paper https://www.microsoft.com/en-us/research/wp-content/uploads/...

"Kinds are calling conventions" paper https://www.microsoft.com/en-us/research/uploads/prod/2019/0...

The -XUnliftedNewtypes extension https://downloads.haskell.org/ghc/latest/docs/html/users_gui...

https://stackoverflow.com/questions/35318562/what-is-levity-...

https://stackoverflow.com/questions/56311510/what-does-type-...

I'm not sure that "evolving" is the right phrase - unlifted types have always been a part of low-level (generally compiler-specific) Haskell.

Can't you just add bang patterns, use deepseq or use the strict/strictdata extension?

There’s a “Stop trying to make Haskell happen, Gretchen - it’s not going to happen!” joke here, somewhere.

He’s ... just not your type?

What Kind of joke is that?

There seems to be a nigh-irresistible urge for people, when explaining type systems, to pick examples that are absolutely useless.

None of the types in the theme here make much sense. They are arbitrary. The contribution to writing a robust program is questionable and they don't do much to explain concepts.

May as well stick with classic "Goats are mammals; that should be enough to get you going with OOP" examples, at least they are less distracting.

I'm not a fan of this article.

That's a problem with the domain itself. Type system examples can be two of: short, concrete, well-motivated. Short concrete examples don't have time for motivation; concrete well-motivated examples require lots of text (or else are unreadable); and short well-motivated examples are forced to be highly abstract.

There's no substitute for actually encountering a real-world problem which makes you want/need type-level programming. The article makes the sensible choice of not trying to invent one for you. I don't think it should be bemoaned for that.

Holy 6MB 2,046px × 1,416px image, Batman!

Yep. Multiples of them totalling 35.4MB of pointless, bandwidth-sucking stupidity.

a testimony on the need to train people to think about memory with lazy fp ?

If by that you mean lazily as in functional programming, I don't see that would help.

OK, I get it finally. Bit thick today! Upvoted.

no worries, humorous comments are not the first expectation on HN

have a nice day

A discussion of the Haskell type system is not what I expected when clicking that link.

Be honest, what was your very first thought?

I did think it was related to functional programming but wasn't entirely sure. It's HN and Americans are asleep, there are less politics and cultural articles.

Kindness may be referring to higher kinded types and for mean girls probably just forced lingo to refer to people who don't take kindly to functional programming and types.

I thought it was going to be a piece in favour of showing kindness to people who themselves are mean.

(I never even considered "this is HN so it's probably tech-related". Don't know what that says about me or the site!)

Yeah, me too. If it wasn't explained in the discussion, I wouldn't click on it. (Maybe HN needs some tags.)

But I am actually glad it's about Haskell, I am a gonna read it now (and it's refreshing to see it being written by woman).

I don't mind the movie references, I don't think it's sexist. (Quite the opposite, I think standard mathematical writing is too dry and benefits from having an unrelated theme to add a bit of spice.)

Current reality is hard for everyone. When men behave like men, some women complain, when women behave like women, some men complain, it's really hard to please everyone. Take it easy, everyone.

The great high school movie with Lindsay Lohan.

> Be honest, what was your very first thought?

Oh My God, neals! you can't just ask people what their first thought was...

Does anyone else think the title is sexist by today's standards?

I have strictly no idea why OP is using women nor in the title or illustrations

It's a jokey reference to the movie Mean Girls (a comedy).

Is mentioning women off limits nowadays? Come on. It might as well been "Kindness for Mean Boys" and the meaning and implications of it would not change a single iota, except losing the movie reference and light tone the author wanted to go for.

I dont have this reference. Kindness for mean boys would have certainly be less controversial but still off topic. Never said that mentioning women is off limits. I don t get why you ask this as an amswer to my statement. Thanks for the movie reference

He's drawing a comparison between Haskell kinds and concepts shown in the (once) popular teenage movie "Mean Girls".

It’s still pretty popular, it does have kind of a cult-movie status.

s/He’s/She’s/

It reinforces the stereotype that only women are mean. I would dislike a title reinforcing stereotypes about me: "Detox for Alcoholic East Europeans: Haskell type enforcement".

No such stereotype says only women are mean.

I've never heard a stereotype that suggests only women are mean. Perhaps it's a cultural trope?

They are referencing the old idea that men handle disagreement with violence while women handle it by being mean to each other. Saying "only women at mean" is hyperbolic, but they likely are stereotypes.

For what it's worth, I've never considered meanness to be limited to non-physical attacks. I'd venture to say a bully punching a kid is just as likely to get labeled mean as a bully that makes fun of a kid.

It's funny how often the people "fighting" a stereotype are the people that bring them up in the first place and thus spread them.

I don't know the movie, so I agree with the title being a bit strange, and I probably could have done with a slightly more factually oriented article, but I appreciate the effort to keep it light. And the stereotypical girls' cliques the article seems to riff on do exist... Girls are known to be more relationally aggressive than boys, who tend to be more physically aggressive than girls. Girls also behave in a more pro-social fashion, so girls' cliques are often larger than boys' cliques, creating more complicated power dynamics. That said, I don't really get what you mean. That's like saying a book called "Good Habits for Incompetent Managers" reinforces the stereotype that only managers are incompetent.

Never heard of a stereotype according to which only women are mean.

It’s just a reference to the Mean Girls movie. Works well with haskell’s kind → mean.

ok I do understand why I didn t understood

Would you like to elaborate how?

Or are you just being pre-emptively offended on someone else's behalf?

Maybe I am a bit over-protective and extrapolate too much, but here is what research says:

"Davies et al. (2002) showed that women experience stereotype threat when they are reminded of existing stereotypes about women in television advertising. In this study, participants watched commercials in which women were very excited about buying cosmetic products or trying a new baking recipe. After watching these commercials, women performed worse on a math test compared with men who watched the same commercials and compared with women who watched gender-neutral commercials."

https://www.frontiersin.org/articles/10.3389/fpsyg.2018.0243...

I just think a more cautious analogy would have made sense.

Stereotype threat is probably not a thing https://www.tandfonline.com/doi/full/10.1080/23743603.2018.1... - publication bias

It's quite sad that this oppression olympics is now poisoning HN's comments section.

It's a stupid title. Connecting the concept to a movie was unnecessary.

But it's not any more sexist than making a movie called (and about) Mean Girls in the first place...

It seems like a decent way to engage women in the content of the article to me. I think that is one of the aims, and why not? The article was written by a woman after all.

True, it just brings back bad memories from EU's "Science: It's a girls thing" campaign.

https://www.theguardian.com/science/blog/2012/jun/29/science...

That initiative is indeed cringeworthy and pandering. But this article feels more organic and genuine, to me. This article was written by a woman software engineer in her own time, and not commissioned by a boardroom full of bureaucrats, maybe that is why.

Err, no? The article is written by a woman, by the way.

not specific to this situation/thread, but women can be sexist too.

It's kinda nerdy and very clickbait-ish but sexist? Probably not, but who am I to judge. Old, white and male means I am not entitled to any opinion on such matters, by today's standards.

Old, white and male — we are probably both plenty entitled. But life is generally favorable to us, so we are often better off listening to those actually affected by this.

Is that to imply less privileged people should feel less obligated to listen or is that to imply more privileged people have less to contribute so they should default to listening? It seems highly unnecessary to devalue large categories of people based on the situations they were born into just to get across a point that listening to others is important.

The principle was merely that people who are not directly affected by X can particularly benefit from listening to people directly affected by X. It was even a supererogatory framing of the recommendation. But enjoy your high horse!

Just because you’re “old, white and male” doesn’t mean you’re not allowed to have an opinion. Don’t let anybody make you feel like that.

I think it was obvious that he doesn't believe that and he's just playing the victim. Nobody in the comments has mentioned anything about white males not having an opinion, and this is a typical argument (and a strawman) that people use to derail the discussion.

No, it's not obvious. You should look at people with a more generous eye and with the benefit of doubt instead of throwing accusations left and right.

Sadly, he's quite on point.

Unless the person believes that old white men literally are not allowed to hold any opinion whatsoever on matters of sexism and that's the most plausible and popular view, then it clearly is both false and a strawman argument, so interpretation doesn't have much to do with it.

There are of course times when modern conversation around this devolve to people saying white men should just shut up, their opinions don't matter, etc. But since there are more defensible, reasonable versions of this (e.g., white men should be more tentative in opinions about discrimination given their relative lack of direct experience of being discriminated against, there are contexts when offering such opinions are inappropriate, etc.), it clearly is a strawman.

For me personal? No.

I think it's a pop culture reference Andi don't think it is sexist.

I thought the pop-culture references were both extremely funny and well-played. It also seems that the author of the post is both a woman and alive in 2020, so no, not at all sexist by today's standards.

The title, I didn’t get. But the sub titles as references to St Paul’s letter to Corinthians? That was slick.

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