10 ms·

Real World Haskell

218 points by Fiveplus 6y ago

srg0 6y ago
I thought it was about the book and almost skipped the link. It would help to name it "Real World Haskell 2020" or something distinct.
- phonebucket 6y ago
  I also thought it was about the book and almost skipped this until reading your comment.
- cies 6y ago
  Think the author should pick new title. This is plain confusing.
- Syzygies 6y ago
  Exactly. The book can't trademark the name in general use, but it's still crappy hygiene to reuse the exact name. This has to be taken as deliberately drafting the wake of the book, which I cannot respect. Nor can the authors feign ignorance. They decided to do this.
miguendes 6y ago
Interesting. I've been programming in python for more than 4 years and I'd like to try something different. I took a haskell class back in the day but just the basics, didn't even learn monads. My goal is not to master the language itself but learn enough to make a better programner. One thing that has been holding me back is the lack of real world examples. I get demotivated when only solving toy problems. This looks like a great resource. I have heard a lot about Haskell From First Principles but there's too much stuff in there.
- girishso 6y ago
  You might want to give a try to Elm. Most of the Haskell goodies but way simpler, except no type classes and too restrictive.
  - dmix 6y ago
    Learning Haskell sideways is a good approach. There are so many usecases in JS as well and Typescript has made it all the better (but not nearly so restrictive).
  - cies 6y ago
    Then PureScript also deserves a mention. It has several frameworks (some akin to the one built in in Elm). If you want to do this in Haskell (which is a lot harder) you may want to look at Miso.
  - tasuki 6y ago
    +1 for Elm to learn Haskell. It is indeed way simpler, and has very friendly error messages. It lets you concentrate on grokking the basics: no side effects, pattern matching, recursion, currying. After some time you start wondering why you have to type `List.map` and `Maybe.map` and `Set.map` when they all do the same thing. Then you'll be ready for some Haskell :)
  - miguendes 6y ago
    Thanks for the suggestion. I've heard people suggesting Elm on reddit but in terms of learning materials there isn't much compared to haskell. But I think that shouldn't be much of a problem. I know that Elm works great for front end but how is it for desktop and backend stuff?
    - piaste 6y ago
      > I know that Elm works great for front end but how is it for desktop and backend stuff? It isn't. It's explicitly designed as a purely web front-end language, that's its scope. Of course, many Elm users like to run another ML-family language in the backend as well. Haskell's Servant backend library, the one used in this article, has a project to automatically generate Elm client code [1]. Elixir is popular as well. But in general, I'd say that any backend framework that can provide an OpenAPI spec will work well, as you'll be able to auto-generate most if not all of the Elm client code (which is normally dull work and one of the main complaints about Elm). [1] https://github.com/haskell-servant/servant-elm https://github.com/haskell-servant/servant-elm
- _query 6y ago
  To build some real world web applications check out IHP: https://ihp.digitallyinduced.com/ https://ihp.digitallyinduced.com/ It's a truly batteries-included way to get started with building real world haskell web apps in minutes.
  - dmix 6y ago
    Wow, if that matures, ie gets some real world adopt by serious companies it would be the best thing around. Much like using Rust and Haskell for web I'd much prefer deferring as much to something like Vue and the server APIs (no sever side rendering for that yet so I mostly just IRL use nuxt.js for toy projects). Something Servant (Haskell) does a clean job of. But you can never completely do away with static heavy lifting This one takes a more modernized Rails or Elixir's Phoenix approach which is really interesting and looks highly usable. Community size and quality is everything for real life software (something I remember Clojure had early on and now Rust has in spades, best of breed sort of libraries to choose from) so I hope it gets some adoption to see where it goes. I'll give it a shot to toy around with when I get some time.
  - anentropic 6y ago
    Step 1: install nix hmm, no thanks
    - justmyname 6y ago
      Install nix? Already done. What's the second step?
    - wtetzner 6y ago
      Why is installing nix any worse than installing some language-specific package manager?
      - whateveracct 6y ago
        Nix causes a visceral negative reaction in some people.
- the5avage 6y ago
  > One thing that has been holding me back is the lack of real world examples. I get demotivated when only solving toy problems. I looked at haskell a few months ago and had a similar problem. While I don't mind the toy problems, all those toy problems have something in common... They can be easily solved with recursion. There are probably patterns to deal with other problems and this would have been more interesting to me. I just had to think to myself: "If all you have is recursion every tutorial looks like a parser" ;)
  - chongli 6y ago
    Recursion is equivalent to iteration. You can solve any problem you like with it. The problem with those tutorials is that they’re trying to do two things at once: 1) teach you Haskell and 2) advocate for Haskell. I’m currently working as a full time assistant for one of the first year computer science courses at my university. This course is taught in a teaching dialect of Racket which does not allow mutation or side effects of any kind. That doesn’t stop the profs from creating assignments with real world applicability such as graffiti stroke recognizers and decision tree learning algorithms. The key is that they’re not trying to make Racket look good, so the patterns of recursion can get pretty ugly at times.
    - the5avage 6y ago
      > Recursion is equivalent to iteration. You can solve any problem you like with it. Maybe my comment was somehow badly written, because you (and the only other reply from chriswarbo) clearly misunderstood me. I know that recursion is equivalent to iteration^^ My point was that some problems fit the one or the other better. Look at fft for example. The algorithm is easy with recursion but hard with iteration. For other problems its the opposite.
      - tasuki 6y ago
        Which problems are hard to solve with recursion instead of iteration?
- WJW 6y ago
  I wrote a blog post some time ago on writing a small URL shortener in Haskell at http://www.wjwh.eu/posts/2019-11-01-haskell-shorturls.html http://www.wjwh.eu/posts/2019-11-01-haskell-shorturls.html. Still a toy example, but more "real world" than recursion exercises :)
allenleein 6y ago
For people who want to dig more, here are some free resources about learning Haskell: https://github.com/allenleein/knowledge-base/tree/gh-pages/%3C00%3E-Functional-Programming https://github.com/allenleein/knowledge-base/tree/gh-pages/%...
- cies 6y ago
  In the real of paid resources, I found this one most useful: https://haskellbook.com https://haskellbook.com
- kimburgess 6y ago
  Also, the unfortunately now de-funded, but still resource bearing https://qfpl.io/projects/professional-fp-courses.html https://qfpl.io/projects/professional-fp-courses.html.
- danidiaz 6y ago
  This is a good way of getting your feet wet: https://haskell-via-sokoban.nomeata.de/ https://haskell-via-sokoban.nomeata.de/
hda111 6y ago
I like how this website gives an overview first on what to expect. I wish more articles shared here would do this.
Ericson2314 6y ago
Ugh, why do we need to spread the world with highly dubious libraries like Esquilito and Servant...
- mrkeen 6y ago
  As a huge fan of Servant, have you got a replacement I should check out?
  - Ericson2314 6y ago
    No ...but I use github.com/obsidiansystems/obelisk/ at work (I work at the place that makes it). It does it's own thing for user-visible routes (for frontend and backend because automatic prerendering). It does a different thing for requests and live queries all of which are over websockets for simplicity. Our routes stuff should be pulled out as a generic dual parsing-prettyprinting library (it and https://hackage.haskell.org/package/tomland https://hackage.haskell.org/package/tomland are the same basic ideal, just need to remove the concrete HTTP / TOML specifics to get to the commonality). I once started throwing together like servant but using data kinds in https://github.com/ericson2314/matrix-client https://github.com/ericson2314/matrix-client
- nimih 6y ago
  What makes those two libraries, in particular, "highly dubious"?
  - Ericson2314 6y ago
    - Persistent: tries to support way to many kinds of databases, ends up being lowest common demoninator dumb about all of them. ---- Just use PostgreSQL simple - Esquilito, not comprehensive. I vaguely remember let through some bad SQL too ---- Use Beam - Servant: the type level stuff is poorly executed nerd skateboarding. It either should be: ---- less type level and more simple-stupid ---- Use data kinds so the type level is less "un-kinded" and catch a lot of mistakes before they become horrible term-level errors.
asplake 6y ago
Immediately confronted by 9 compiler extension directives, major turnoff to this interested newbie. Is this considered normal and acceptable?
- aszen 6y ago
  I think this is considered normal for real world Haskell usage. Most libraries and even frameworks like ihp that try to be favor ease of use rely on these language extensions. You can ofcourse place these directives once in the cabal file, but there's no getting around to learning what they do.
- tome 6y ago
  Why a turnoff? "Extension" just means "language feature that is thoroughly well-specified, well-tested and widely used but hasn't made it into the language standard (partly because there hasn't been one for ten years)".
- lallysingh 6y ago
  Yes. They're normal here, and you can consider them about as significant as an import statement, some context when reading the code, but nothing crazy. The extensions are very well vetted, and new versions of the language standard can be summed up as "enable extensions a, b, c by default." Plus library changes, of course.
- kccqzy 6y ago
  Are you looking at production code or pedagogical examples? For the former, it's totally normally to use compiler-specific features. If you are scared off by that, you'd be better served reading a book that introduces things little by little.
- iso8859-1 6y ago
  With GHC2021, you may soon be able to simply put that instead, and it will imply enabling all those individually. https://www.reddit.com/r/haskell/comments/je1t82/does_the_idea_of_xghc2021_excite_you/ https://www.reddit.com/r/haskell/comments/je1t82/does_the_id...
- 6y ago
aszen 6y ago
In my brief experience of going through the Haskell examples, I am awestruck by the power that Haskell enables yet scared by the huge type level complexity underlying the libraries that enable it. Just to query a database the example used half a dozen langauge extensions. I could probably learn the base Haskell langauge but that's not enough it seems for real world usage. Now these langauge extensions ofcourse reduce the boilerplate and enable a nicer syntax but they dramatically increase the cost of using Haskell in production. My understanding of the ecosystem is that there is a divide between people who want to use Simple Haskell concepts and others that want to advance the state of the start for every library. https://www.simplehaskell.org/ https://www.simplehaskell.org/
- strbean 6y ago
  I worked with Haskell for awhile but never had it fully 'click'. That being said, I think that once someone is fully comfortable with algebraic data types, category theory, and functional programming, most of these extensions and fancy constructs become pretty shallow and easy to understand. (Would appreciate if any bonafide haskellers care to comment)
  - carterschonwald 6y ago
    Cat theory isn’t needed at all. It just gives you another smell test for recognizing you maybe designed an api nicely. (Aka: oh cool, my api code has some nice mathematical / logical property, maybe it’s not just mud on the wall)
    - tiew9Vii 6y ago
      Agree. You don’t need to know category theory to use Haskell or the libraries. Know category theory or being aware of it just gives you a deeper understanding of the way things work. I don’t know category theory but aware of it. The way I look at it is c style languages you have design patterns. These are loosely designed patterns with no formal definitions. That makes it hard to reason about or test things. In category theory you have mathematical laws. Laws are far stronger than a loosely typed designed patterns so using these laws it’s far easier to reason about code.
mraza007 6y ago
Can anyone share where’s haskell used Like what companies are using haskell
- elbear 6y ago
  Github are using it https://github.com/github/semantic https://github.com/github/semantic Facebook and many others.
ajarmst 6y ago
I'm not convinced that arguing that "think[ing] day-to-day tasks like running a web app are difficult or impossible in Haskell! ... isn't true!" is well-served by a series that introduces (in the first post!) Persist and Template Haskell and then has {-# LANGUAGE TemplateHaskell #-} {-# LANGUAGE QuasiQuotes #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE GeneralizedNewtypeDeriving #-} {-# LANGUAGE RecordWildCards #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE OverloadedStrings #-} PTH.share [PTH.mkPersist PTH.sqlSettings, PTH.mkMigrate "migrateAll"] [PTH.persistLowerCase| User sql=users name Text email Text age Int occupation Text UniqueEmail email deriving Show Read |] as literally the third block of code in the series. That's more of a proof of the opposite, don't you think?
- saithound 6y ago
  Python web app tutorials routinely introduce MongoDB/pymongo, Flask, at-annotations for routing, and follow that up with 2-5 `from __future__ import` statements. These are pretty much exactly analogous to the steps in the current series. The only difference is that the Haskell standards change less frequently, so more "from __future__" imports (LANGUAGE pragmas) are required. (Note that the latest Haskell is from 2010, while the latest Python is from 31 days ago; see how many future imports you need to get a modern Python web app to work with a ten year old Python release) This is not evidence that day-to-day tasks like running a web app are difficult or impossible in Python.
  - momentoftop 6y ago
    This code relies on GHC and GHC specific extensions. The mentioned pragmas are not defined by the 2010 standard. The lastest GHC release is from August 8th of this year.
    - saithound 6y ago
      > The mentioned pragmas are not defined by the 2010 standard. That's exactly the point. GHC supports the most recent Haskell version it supports, and implements some extensions to the standard language, which can all be enabled or disabled using compiler directives (LANGUAGE pragmas). These are analogous to Python future import statements, which are compiler directive saying that a particular module should be compiled using syntax or semantics that is not part of the current version of Python the language. Once in a blue moon, the Haskell standard changes, and certain features that you used pragmas for (e.g. PatternGuards, EmptyDataDecls, RelaxedPolyRec) will no longer require them. This depends on the standard, not the latest GHC release. Unlike Python, core Haskell changes slowly and conservatively, so you should not be surprised that the average Haskell code uses pragmas more frequently than Python uses future imports.

218 points by Fiveplus 6y ago

srg0 6y ago

I thought it was about the book and almost skipped the link. It would help to name it "Real World Haskell 2020" or something distinct.

phonebucket 6y ago
I also thought it was about the book and almost skipped this until reading your comment.
cies 6y ago
Think the author should pick new title. This is plain confusing.
Syzygies 6y ago
Exactly. The book can't trademark the name in general use, but it's still crappy hygiene to reuse the exact name. This has to be taken as deliberately drafting the wake of the book, which I cannot respect. Nor can the authors feign ignorance. They decided to do this.

miguendes 6y ago

Interesting. I've been programming in python for more than 4 years and I'd like to try something different. I took a haskell class back in the day but just the basics, didn't even learn monads. My goal is not to master the language itself but learn enough to make a better programner. One thing that has been holding me back is the lack of real world examples. I get demotivated when only solving toy problems. This looks like a great resource. I have heard a lot about Haskell From First Principles but there's too much stuff in there.

girishso 6y ago
You might want to give a try to Elm. Most of the Haskell goodies but way simpler, except no type classes and too restrictive.
- dmix 6y ago
  Learning Haskell sideways is a good approach. There are so many usecases in JS as well and Typescript has made it all the better (but not nearly so restrictive).
- cies 6y ago
  Then PureScript also deserves a mention. It has several frameworks (some akin to the one built in in Elm). If you want to do this in Haskell (which is a lot harder) you may want to look at Miso.
- tasuki 6y ago
  +1 for Elm to learn Haskell. It is indeed way simpler, and has very friendly error messages. It lets you concentrate on grokking the basics: no side effects, pattern matching, recursion, currying. After some time you start wondering why you have to type `List.map` and `Maybe.map` and `Set.map` when they all do the same thing. Then you'll be ready for some Haskell :)
- miguendes 6y ago
  Thanks for the suggestion. I've heard people suggesting Elm on reddit but in terms of learning materials there isn't much compared to haskell. But I think that shouldn't be much of a problem. I know that Elm works great for front end but how is it for desktop and backend stuff?
  - piaste 6y ago
    > I know that Elm works great for front end but how is it for desktop and backend stuff? It isn't. It's explicitly designed as a purely web front-end language, that's its scope. Of course, many Elm users like to run another ML-family language in the backend as well. Haskell's Servant backend library, the one used in this article, has a project to automatically generate Elm client code [1]. Elixir is popular as well. But in general, I'd say that any backend framework that can provide an OpenAPI spec will work well, as you'll be able to auto-generate most if not all of the Elm client code (which is normally dull work and one of the main complaints about Elm). [1] https://github.com/haskell-servant/servant-elm https://github.com/haskell-servant/servant-elm
_query 6y ago
To build some real world web applications check out IHP: https://ihp.digitallyinduced.com/ https://ihp.digitallyinduced.com/ It's a truly batteries-included way to get started with building real world haskell web apps in minutes.
- dmix 6y ago
  Wow, if that matures, ie gets some real world adopt by serious companies it would be the best thing around. Much like using Rust and Haskell for web I'd much prefer deferring as much to something like Vue and the server APIs (no sever side rendering for that yet so I mostly just IRL use nuxt.js for toy projects). Something Servant (Haskell) does a clean job of. But you can never completely do away with static heavy lifting This one takes a more modernized Rails or Elixir's Phoenix approach which is really interesting and looks highly usable. Community size and quality is everything for real life software (something I remember Clojure had early on and now Rust has in spades, best of breed sort of libraries to choose from) so I hope it gets some adoption to see where it goes. I'll give it a shot to toy around with when I get some time.
- anentropic 6y ago
  Step 1: install nix hmm, no thanks
  - justmyname 6y ago
    Install nix? Already done. What's the second step?
  - wtetzner 6y ago
    Why is installing nix any worse than installing some language-specific package manager?
    - whateveracct 6y ago
      Nix causes a visceral negative reaction in some people.
the5avage 6y ago
> One thing that has been holding me back is the lack of real world examples. I get demotivated when only solving toy problems. I looked at haskell a few months ago and had a similar problem. While I don't mind the toy problems, all those toy problems have something in common... They can be easily solved with recursion. There are probably patterns to deal with other problems and this would have been more interesting to me. I just had to think to myself: "If all you have is recursion every tutorial looks like a parser" ;)
- chongli 6y ago
  Recursion is equivalent to iteration. You can solve any problem you like with it. The problem with those tutorials is that they’re trying to do two things at once: 1) teach you Haskell and 2) advocate for Haskell. I’m currently working as a full time assistant for one of the first year computer science courses at my university. This course is taught in a teaching dialect of Racket which does not allow mutation or side effects of any kind. That doesn’t stop the profs from creating assignments with real world applicability such as graffiti stroke recognizers and decision tree learning algorithms. The key is that they’re not trying to make Racket look good, so the patterns of recursion can get pretty ugly at times.
  - the5avage 6y ago
    > Recursion is equivalent to iteration. You can solve any problem you like with it. Maybe my comment was somehow badly written, because you (and the only other reply from chriswarbo) clearly misunderstood me. I know that recursion is equivalent to iteration^^ My point was that some problems fit the one or the other better. Look at fft for example. The algorithm is easy with recursion but hard with iteration. For other problems its the opposite.
    - tasuki 6y ago
      Which problems are hard to solve with recursion instead of iteration?
WJW 6y ago
I wrote a blog post some time ago on writing a small URL shortener in Haskell at http://www.wjwh.eu/posts/2019-11-01-haskell-shorturls.html http://www.wjwh.eu/posts/2019-11-01-haskell-shorturls.html. Still a toy example, but more "real world" than recursion exercises :)

allenleein 6y ago

For people who want to dig more, here are some free resources about learning Haskell: https://github.com/allenleein/knowledge-base/tree/gh-pages/%3C00%3E-Functional-Programming https://github.com/allenleein/knowledge-base/tree/gh-pages/%...

cies 6y ago
In the real of paid resources, I found this one most useful: https://haskellbook.com https://haskellbook.com
kimburgess 6y ago
Also, the unfortunately now de-funded, but still resource bearing https://qfpl.io/projects/professional-fp-courses.html https://qfpl.io/projects/professional-fp-courses.html.
danidiaz 6y ago
This is a good way of getting your feet wet: https://haskell-via-sokoban.nomeata.de/ https://haskell-via-sokoban.nomeata.de/

hda111 6y ago

I like how this website gives an overview first on what to expect. I wish more articles shared here would do this.

Ericson2314 6y ago

Ugh, why do we need to spread the world with highly dubious libraries like Esquilito and Servant...

mrkeen 6y ago
As a huge fan of Servant, have you got a replacement I should check out?
- Ericson2314 6y ago
  No ...but I use github.com/obsidiansystems/obelisk/ at work (I work at the place that makes it). It does it's own thing for user-visible routes (for frontend and backend because automatic prerendering). It does a different thing for requests and live queries all of which are over websockets for simplicity. Our routes stuff should be pulled out as a generic dual parsing-prettyprinting library (it and https://hackage.haskell.org/package/tomland https://hackage.haskell.org/package/tomland are the same basic ideal, just need to remove the concrete HTTP / TOML specifics to get to the commonality). I once started throwing together like servant but using data kinds in https://github.com/ericson2314/matrix-client https://github.com/ericson2314/matrix-client
nimih 6y ago
What makes those two libraries, in particular, "highly dubious"?
- Ericson2314 6y ago
  - Persistent: tries to support way to many kinds of databases, ends up being lowest common demoninator dumb about all of them. ---- Just use PostgreSQL simple - Esquilito, not comprehensive. I vaguely remember let through some bad SQL too ---- Use Beam - Servant: the type level stuff is poorly executed nerd skateboarding. It either should be: ---- less type level and more simple-stupid ---- Use data kinds so the type level is less "un-kinded" and catch a lot of mistakes before they become horrible term-level errors.

asplake 6y ago

Immediately confronted by 9 compiler extension directives, major turnoff to this interested newbie. Is this considered normal and acceptable?

aszen 6y ago
I think this is considered normal for real world Haskell usage. Most libraries and even frameworks like ihp that try to be favor ease of use rely on these language extensions. You can ofcourse place these directives once in the cabal file, but there's no getting around to learning what they do.
tome 6y ago
Why a turnoff? "Extension" just means "language feature that is thoroughly well-specified, well-tested and widely used but hasn't made it into the language standard (partly because there hasn't been one for ten years)".
lallysingh 6y ago
Yes. They're normal here, and you can consider them about as significant as an import statement, some context when reading the code, but nothing crazy. The extensions are very well vetted, and new versions of the language standard can be summed up as "enable extensions a, b, c by default." Plus library changes, of course.
kccqzy 6y ago
Are you looking at production code or pedagogical examples? For the former, it's totally normally to use compiler-specific features. If you are scared off by that, you'd be better served reading a book that introduces things little by little.
iso8859-1 6y ago
With GHC2021, you may soon be able to simply put that instead, and it will imply enabling all those individually. https://www.reddit.com/r/haskell/comments/je1t82/does_the_idea_of_xghc2021_excite_you/ https://www.reddit.com/r/haskell/comments/je1t82/does_the_id...
6y ago

aszen 6y ago

In my brief experience of going through the Haskell examples, I am awestruck by the power that Haskell enables yet scared by the huge type level complexity underlying the libraries that enable it. Just to query a database the example used half a dozen langauge extensions. I could probably learn the base Haskell langauge but that's not enough it seems for real world usage. Now these langauge extensions ofcourse reduce the boilerplate and enable a nicer syntax but they dramatically increase the cost of using Haskell in production. My understanding of the ecosystem is that there is a divide between people who want to use Simple Haskell concepts and others that want to advance the state of the start for every library. https://www.simplehaskell.org/ https://www.simplehaskell.org/

strbean 6y ago
I worked with Haskell for awhile but never had it fully 'click'. That being said, I think that once someone is fully comfortable with algebraic data types, category theory, and functional programming, most of these extensions and fancy constructs become pretty shallow and easy to understand. (Would appreciate if any bonafide haskellers care to comment)
- carterschonwald 6y ago
  Cat theory isn’t needed at all. It just gives you another smell test for recognizing you maybe designed an api nicely. (Aka: oh cool, my api code has some nice mathematical / logical property, maybe it’s not just mud on the wall)
  - tiew9Vii 6y ago
    Agree. You don’t need to know category theory to use Haskell or the libraries. Know category theory or being aware of it just gives you a deeper understanding of the way things work. I don’t know category theory but aware of it. The way I look at it is c style languages you have design patterns. These are loosely designed patterns with no formal definitions. That makes it hard to reason about or test things. In category theory you have mathematical laws. Laws are far stronger than a loosely typed designed patterns so using these laws it’s far easier to reason about code.

mraza007 6y ago

Can anyone share where’s haskell used Like what companies are using haskell

elbear 6y ago
Github are using it https://github.com/github/semantic https://github.com/github/semantic Facebook and many others.

ajarmst 6y ago

I'm not convinced that arguing that "think[ing] day-to-day tasks like running a web app are difficult or impossible in Haskell! ... isn't true!" is well-served by a series that introduces (in the first post!) Persist and Template Haskell and then has {-# LANGUAGE TemplateHaskell #-} {-# LANGUAGE QuasiQuotes #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE GeneralizedNewtypeDeriving #-} {-# LANGUAGE RecordWildCards #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE OverloadedStrings #-} PTH.share [PTH.mkPersist PTH.sqlSettings, PTH.mkMigrate "migrateAll"] [PTH.persistLowerCase| User sql=users name Text email Text age Int occupation Text UniqueEmail email deriving Show Read |] as literally the third block of code in the series. That's more of a proof of the opposite, don't you think?

saithound 6y ago
Python web app tutorials routinely introduce MongoDB/pymongo, Flask, at-annotations for routing, and follow that up with 2-5 `from __future__ import` statements. These are pretty much exactly analogous to the steps in the current series. The only difference is that the Haskell standards change less frequently, so more "from __future__" imports (LANGUAGE pragmas) are required. (Note that the latest Haskell is from 2010, while the latest Python is from 31 days ago; see how many future imports you need to get a modern Python web app to work with a ten year old Python release) This is not evidence that day-to-day tasks like running a web app are difficult or impossible in Python.
- momentoftop 6y ago
  This code relies on GHC and GHC specific extensions. The mentioned pragmas are not defined by the 2010 standard. The lastest GHC release is from August 8th of this year.
  - saithound 6y ago
    > The mentioned pragmas are not defined by the 2010 standard. That's exactly the point. GHC supports the most recent Haskell version it supports, and implements some extensions to the standard language, which can all be enabled or disabled using compiler directives (LANGUAGE pragmas). These are analogous to Python future import statements, which are compiler directive saying that a particular module should be compiled using syntax or semantics that is not part of the current version of Python the language. Once in a blue moon, the Haskell standard changes, and certain features that you used pragmas for (e.g. PatternGuards, EmptyDataDecls, RelaxedPolyRec) will no longer require them. This depends on the standard, not the latest GHC release. Unlike Python, core Haskell changes slowly and conservatively, so you should not be surprised that the average Haskell code uses pragmas more frequently than Python uses future imports.