Hacker News Reader

Comment by lylecubed | Hacker News Reader

> An introduction to dependent types, demonstrating the most beautiful aspects, one step at a time.

Is there a companion book detailing the ugly downsides of dependent types and how to avoid them, one step at a time?

I feel like people are misreading this comment, which is asking how to avoid the pitfalls of dependent types, not how to avoid dependent types.

This. Thank you. I'm being rate limited, so this is the only post I'll be making on this thread. My question was genuine. I want to learn both the positives and the pitfalls of dependent types. I mimicked the book's description because it amused me from a linguistic perspective. Looking back, I probably should have phrased it differently.

> the ugly downsides of dependent types and how to avoid them

There's this Reddit answer from two years ago, and the subsequent comments https://www.reddit.com/r/haskell/comments/3zc81v/tradeoffs_o...

This is exactly what I'm looking for. Thanks!

Note that many of those problems are being actively worked on in research, and progress is being made, albeit slowly. That said, we can still get some of the benefits of dependent types, even without all the problems being solved right now! Just gotta be aware that it's not all roses yet.

Can you elaborate? Do you have war stories?

Here is a quick guide to avoiding them: "Unless you are using Haskell at a very high level of abstraction, Coq, Agda, Pie or Idris: congratulations you have avoided them."

It's not really clear why you'd want a book about the downsides of a quite recent development in practically usable programming models. Is it just because you are a hater?

My guess is because OP has been burned by the "LEARN THIS NEW THING, IT'S REALLY COOL AND POWERFUL AND ALL OF THE COOL KIDS ARE DOING IT (and oh by the way many of the simple things you do all the time are incredibly inconvenient...)" narrative one too many times.

Adopting something purely on it's merits is a bad idea, but nobody ever writes the book about a language/paradigm's downsides. I'm pretty sure that was the joke, but I might be off.

Unless said language is PHP, in which case there's no end of diatribes about it

nobody ever writes the book about a language/paradigm's downsides

Indeed. One can argue that books like "optimizing X" or "secure X" are about ways to easily write slow or insecure code in X, but this is somewhat narrow. Is there never enough demand for a broader book on downsides of X?

Bertrand Meyer's book on Eiffel was all about the downsides of C++.

And then there's the Unix-Hater's Handbook...

https://en.wikipedia.org/wiki/The_Unix-Haters_Handbook

I wrote a whole chapter about the downsides of X -- do you think there's a need for a broader book? ;)

https://medium.com/@donhopkins/the-x-windows-disaster-128d39...

The one where you demonstrated that you don't know the difference between a client and a server? :-)

How's it "not knowing the difference" to explain that the usage of the terms client and server switched over time, in the sense of which is local and which is remote?

An xterm client running on a VAX mainframe connects to an X11 server running on a Sun workstation: the X11 client is remote, the X11 server is local.

A web browser client running on a phone connects to a web server running in the cloud: the web client is local, the web server is remote.

Right?

Loled. I used to do phone support for x11 servers for pcs. This terminology confused people to no end

Exactly! I, too, used to live in an office next to a machine room full of "web clients"! :-D

(Actually, I'm one of those deluded fools who claim a "server" provides a "service" to one or more "clients", who make "requests". Yeah, I know, but I figure somebody has to keep the joke funny.)

Here's how Jim Fulton (who wrote the early graphics drivers for X6) explains it:

https://www.quora.com/profile/Jim-Fulton

https://www.quora.com/Why-is-the-X-Windows-architecture-clie...

>Given it's roots, X naturally used the technically-correct terms to describe its major components: the portion that abstracted display and input hardware into a service that could be used by other programs was called the "display server"; the portion that made use of those services was called the "display client." This later caused endless confusion who thought that "server" was a synonym for "big computer" (file server, database server, etc.) and "client" meant "small computer" (diskless client, etc.). Who knows, maybe it would have been easier had they been called "application server" and "application client" but that revisionist history.

Also interesting:

>Ultimately, the pendulum swung back with the advent of Web 2.0 technology and mobile devices. Now, we take it for granted that applications can run anywhere in the network and be accessed by any type of device. While X is primitive compared to JavaScript and HTML5 (whose ability to push computational tasks over the network into the display device were inspired by Java and NeWS), X did lay the initial groundwork. It also proved that an open source model could work for in business environments. Not too shabby for a technology that will soon be hitting its 30th anniversary.

>Jim Fulton, alumnus of Project Athena, the MIT X Consortium, Cognition (first commercial use of X on DOS) and Network Computing Devices (leading X terminal vendor)

> I wrote a whole chapter about the downsides of X

I lol'ed 6-8 times... Still, I have to say that I'm loving my distros lately; distro maintainers, you rule!

Some typos in the article:

eents/events client an/client can because it the/because it solved? the tires/tries ore dump/core dump trwe/tree piel/pixel resulution/resolution ertain/certain N ot/Not screens een have/screens have

There are tons, but we really need to ask if any of this is a fair topic for Dependent Typing, which has only emerged from pi-calculus musings on paper to compilers that can do more than prove simple structural recursion.

It's like seeing a photo of a baby and asking why there isn't a service to provide police records for babies, because you "just want to be careful, you know?"

Here's one for JS http://johnkpaul.github.io/presentations/empirejs/javascript...

It's not even really possible to "adopt" dependent typing today. It's only emerged from the realm of academic curiosity and only two implementations exist that are anywhere near "practical" in the context you're describing.

Both of those implementations are very honest about their shortcomings, and nearly every talk and blogpost for them mentions you can't yet use this in many industrial contexts.

It's very difficult to see this as anything but the usual distate for PL theory that constantly swirls around this community. If the author didn't intend to associate a post with that, then they've done it by accident.

>only two implementations exist that are anywhere near "practical"

Out of curiosity, why F* or Idris are not practical?

F* and Idris are precisely the ones I had in mind, although I guess you could make an argument for Agda.

What did you think I was imagining? I can only name 5 DT languages off the top of my head.

So, why are they not practical in your opinion?

Reply on news.ycombinator.com