10 ms·

Reading Simple Haskell

161 points by Tehnix 9y ago

Tehnix 9y ago
Unrelated: I'm obviously quite biased, but I generally like Haskell code for pseudo code like things, because it does away with a lot of syntax specific cruft, and stays close to the math it's usually talking about. Also, readers might be interested in A Tour of Go in Haskell, which is the concurrency chapter of A Tour of Go, but just...in Haskell - https://a-tour-of-go-in-haskell.syocy.net/en_US/index.html https://a-tour-of-go-in-haskell.syocy.net/en_US/index.html.
- spraak 9y ago
  Wow that resource is super clever and useful, I wish it had the full "Tour"!
  - Tehnix 9y ago
    It was more or less just posted, but I could imagine there is plans for the rest of the content to be ported also. I might help with that if I get any time during Christmas :x
- pjmlp 9y ago
  Regarding concurrency in Haskell, there is a very good book from Simon Marlow, "Parallel and Concurrent Programming in Haskell".
- deleted 9y ago
  [deleted]
- hoprocker 9y ago
  Agreed -- I found Haskell most confusing at first because of the lack of syntax. My brain kept wondering where the rest of the syntax was. Not to be too dramatic, but I think Haskell is kind of like programming "poetry" in this regard.
  - leshow 9y ago
    When I first start I though there was so MUCH syntax, (->), (<*>), (<$>), (>>=), (.), ($), etc I realized pretty early on all these were just functions, that was cool experience for me. Even the types are sort of functions.
    - lalaithion 9y ago
      One fun thing is how -> is basically just an infix operation that takes two types as arguments and returns a new type. add :: (->) Int Int add x y = x + y
      - leshow 9y ago
        It's the function type, data (->) a b. It is commonly written in infix notation though.
- junkscience2017 9y ago
  Go is impoverished compared to Haskell but not when it comes to concurrency. The Haskell analogues for these concurrency primitives seem laborious...and they were even moreso prior to the advent of the `async` library.
  - Tehnix 9y ago
    A commenter on /r/haskell[0] noted that there is actually a library that mimics Go Channels a bit closer, called GoChan[1]. That said, I think `async` is the idiomatic choice, so it probably makes more sense to keep it. [0] https://www.reddit.com/r/haskell/comments/7ilhb9/a_tour_of_go_in_haskell/ https://www.reddit.com/r/haskell/comments/7ilhb9/a_tour_of_g... [1] https://hackage.haskell.org/package/gochan-0.0.2/docs/Control-Concurrent-GoChan.html https://hackage.haskell.org/package/gochan-0.0.2/docs/Contro...
  - bjoli 9y ago
    Which is strange. It should be possible to implement proper CML-style concurrency in Haskell, which is strictly more expressive than the go concurrency model.
speps 9y ago
I only started Haskell since the 1st day of Advent of Code this year. I didn't see that mentioned much either in the article or other articles, but Haskell is like Python and has significant whitespace to determine scope. The error messages related to this aren't always clear...
- Tehnix 9y ago
  The error messages should have improved a bit with GHC 8.2[0], you might wanna check that out if you aren't already using it. For stack that'll mean using the nightlies though (e.g. `resolver: nightly-2017-12-09`). [0] https://twitter.com/raichoo/status/825045995490795521 https://twitter.com/raichoo/status/825045995490795521
culturedsystems 9y ago
One thing this doesn't mention, which might be useful to know, is that Haskell is indentation-sensitive. For instance, those examples using "let" won't compile if the lines beginning with "let" and "in" aren't indented. I'd be interested if anyone knows of a simple guide to Haskell's indentation rules - I still find it trips me up now and then.
- tome 9y ago
  > I'd be interested if anyone knows of a simple guide to Haskell's indentation rules - I still find it trips me up now and then. The "simple" way I deal with it is to use Emacs and press TAB until things look right :)
- Tehnix 9y ago
  Re indentation, you might find these two useful https://en.wikibooks.org/wiki/Haskell/Indentation https://en.wikibooks.org/wiki/Haskell/Indentation and http://echo.rsmw.net/n00bfaq.html http://echo.rsmw.net/n00bfaq.html.
  - kkmx 9y ago
    That helped thanks!
- masklinn 9y ago
  > Haskell is indentation-sensitive. That's not really true, at least not in the way Python is. Haskell is actually defined using "braceful" syntax, and that syntax can be used anywhere (and is useful for code generation); on top of that it has Layout Rules[0]. Basically: Any time a "where", "let", "do" or "of" keyword is not followed by a brace, an implicit one is inserted and the indentation of the next lexeme (non-comment non-whitespace item) is noted[1] For any subsequent line, * if it's indented by the same amount as the one noted, a semi-colon is prepended * if it's indented by less than the noted amount, a closing brace is prepended A closing brace is also inserted when encountering an illegal lexeme (for the current structure) where a a closing brace would be legal. [0] https://www.haskell.org/onlinereport/haskell2010/haskellch2.html#x7-210002.7 https://www.haskell.org/onlinereport/haskell2010/haskellch2.... [1] except if the indentation of the next non-whitespace lexeme is less than the current indentation level, then an empty block is inserted, and layout processing for the current scope continues
mark_l_watson 9y ago
Nice guide for learning to read Haskell code! You have one minor type: "tree1123 :: IntTree tree ="
- gilmi 9y ago
  thanks! fixed.
hellofunk 9y ago
I once downloaded a python script, ran it with some input, and got a result. Curious, I opened the script in Emacs, which then opened it into python mode. As is my habit, I indented the whole file, which did basic white space changes to it according to python mode. I didn't realize I did this at first, and I saved and exited the script, then played around with it some more. Still got results, everything seemed the same. But when I tried it with the same input as originally, it was a different return result. This took a while to figure out, until I realized that emacs changed the indentation of just one line, because the author had apparently not followed the typical idioms or conventions of indenting python in some way. That merely opening, beautifying, and saving a file could change program output with no errors has turned me off of white space sensitive syntax ever since. Which is partly why OCaml gets some bias from me over Haskell.
- mlevental 9y ago
  honestly it's bananas. I can't for the life of understand how such a poor form over function decision was ever made by an engineer. the number of bugs (>0) this introduces into production code every year is reason enough (imho the only relevant metric) to prefer braces. are block delimiting braces really that onerous???
  - coldtea 9y ago
    Because braces don't introduce bugs? You can just as easily omit braces in a if/for etc statement and have a bug, or close the wrong brace at the wrong point (and also introduce a bug).
    - mlevental 9y ago
      >omit braces so you're saying braceless ifs and fors are bad? yes I agree. > close the wrong brace -/+ 1 flipping the right number of braces to get that kind of bug is much much harder than indenting a block incorrectly
      - avmich 9y ago
_0ffh 9y ago
This site breaks the zoom function in Firefox. Please be considerate towards the visually impaired, and don't break zoom on one of the few browsers that actually even have a somewhat useful zoom function!
- quadrangle 9y ago
  While I agree STRONGLY, I just tested after seeing your comment and it led me to try the Reader mode in FF which worked perfectly and thus allows full zooming of this site.
  - _0ffh 9y ago
    Wow, thank you for introducing me to that feature!
- sridca 9y ago
  It doesn’t even work on iOS safari.
  - gilmi 9y ago
    You can view this as markdown on github[0] [0]: https://github.com/soupi/rfc/blob/master/reading_haskell.md https://github.com/soupi/rfc/blob/master/reading_haskell.md
- gilmi 9y ago
  I'm sorry for that. I'll try to fix this when I can. For now you can view the markdown document instead of the slides here: https://github.com/soupi/rfc/blob/master/reading_haskell.md https://github.com/soupi/rfc/blob/master/reading_haskell.md
bachmeier 9y ago
Haskell is one of the few major languages I haven't used much. I find this to be very helpful. Sometimes I look at the Pandoc source and wonder what the hell I'm looking at.
swlkr 9y ago
I've always been confused when reading Haskell snippets on the web, this really cleared things up for me!
cygned 9y ago
x +- y = (x + x) - (y + y) That's crazy. I should learn Haskell (again).
- mlevental 9y ago
  what exactly is crazy about this?
  - runeks 9y ago
    The simplicity with which a new operator is defined.
    - cygned 9y ago
      This. Incredible elegant. I always enjoy these types of things when programming Lisp.
    - akhilcacharya 9y ago
      I think this is a downside. It just makes reading new code that uses esoteric symbols defined elsewhere.
      - gilmi 9y ago
        This[0] operator glossary reviews the most used operators. [0]: https://haskell-lang.org/tutorial/operators https://haskell-lang.org/tutorial/operators
- Tehnix 9y ago
  `+-` here is an entirely new operator though. The shuffling of arguments might look a bit weird though, it could also be written (+-) x y = (x + x) - (y + y) Symbol operators are automatically infix though, and you can make them normal using (), same as backticks make normal functions infix, `a la 2 `plus` 3.
notsgnik 9y ago
nice guide
weavie 9y ago
Haskell can be very readable and elegant, but what I do find frustrating is when research papers show sample Haskell, but it's not quite Haskell. They just can't seem to resist the urge to replace various operators and types with their own non-alphanumeric symbols, thus making what should be reading simple code into some kind of hieroglyphic translation exercise..
- leshow 9y ago
  There are a bunch build into the language, I think a lot of libraries take their queue from there. Still, after you get over the initial hurdle of like <$> == fmap. It's not so bad.
- nybble41 9y ago
  > when research papers show sample Haskell, but it's not quite Haskell For the most part the code in the research papers actually _is_ valid Haskell, provided you enable the -XUnicodeSyntax extension and include a few extra modules. Haskell 98 permits Unicode symbols and identifiers; the extension covers the handful of symbols which are built in to the language or enabled by other extensions. You can find a full list here: https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/glasgow_exts.html#unicode-syntax https://downloads.haskell.org/~ghc/latest/docs/html/users_gu... Personally I prefer Unicode symbols and tend to use them whenever possible. I have some XCompose rules configured to make them easier to type. Unfortunately, I have yet to find a comparable input system for Windows.
nigwil_ 9y ago
I like the content but: I can't link to the slide because of the way these pages are defined: slide 11: The presented argument order in the ASCII-art of Red, Blue, Green I think should be Red, Green, Blue to match the usual initialism. I could not find a way to submit a pull-request for this presentation, and my search-fu on github failed to find the associated repo, and there were no links I could find in the presentation to submit comments.
- gilmi 9y ago
  Thanks! fixed. You can find the document and repo here: https://github.com/soupi/rfc/blob/master/reading_haskell.md https://github.com/soupi/rfc/blob/master/reading_haskell.md

161 points by Tehnix 9y ago

Unrelated: I'm obviously quite biased, but I generally like Haskell code for pseudo code like things, because it does away with a lot of syntax specific cruft, and stays close to the math it's usually talking about. Also, readers might be interested in A Tour of Go in Haskell, which is the concurrency chapter of A Tour of Go, but just...in Haskell - https://a-tour-of-go-in-haskell.syocy.net/en_US/index.html https://a-tour-of-go-in-haskell.syocy.net/en_US/index.html.

spraak 9y ago
Wow that resource is super clever and useful, I wish it had the full "Tour"!
- Tehnix 9y ago
  It was more or less just posted, but I could imagine there is plans for the rest of the content to be ported also. I might help with that if I get any time during Christmas :x
pjmlp 9y ago
Regarding concurrency in Haskell, there is a very good book from Simon Marlow, "Parallel and Concurrent Programming in Haskell".
deleted 9y ago
[deleted]
hoprocker 9y ago
Agreed -- I found Haskell most confusing at first because of the lack of syntax. My brain kept wondering where the rest of the syntax was. Not to be too dramatic, but I think Haskell is kind of like programming "poetry" in this regard.
- leshow 9y ago
  When I first start I though there was so MUCH syntax, (->), (<*>), (<$>), (>>=), (.), ($), etc I realized pretty early on all these were just functions, that was cool experience for me. Even the types are sort of functions.
  - lalaithion 9y ago
    One fun thing is how -> is basically just an infix operation that takes two types as arguments and returns a new type. add :: (->) Int Int add x y = x + y
    - leshow 9y ago
      It's the function type, data (->) a b. It is commonly written in infix notation though.
junkscience2017 9y ago
Go is impoverished compared to Haskell but not when it comes to concurrency. The Haskell analogues for these concurrency primitives seem laborious...and they were even moreso prior to the advent of the `async` library.
- Tehnix 9y ago
  A commenter on /r/haskell[0] noted that there is actually a library that mimics Go Channels a bit closer, called GoChan[1]. That said, I think `async` is the idiomatic choice, so it probably makes more sense to keep it. [0] https://www.reddit.com/r/haskell/comments/7ilhb9/a_tour_of_go_in_haskell/ https://www.reddit.com/r/haskell/comments/7ilhb9/a_tour_of_g... [1] https://hackage.haskell.org/package/gochan-0.0.2/docs/Control-Concurrent-GoChan.html https://hackage.haskell.org/package/gochan-0.0.2/docs/Contro...
- bjoli 9y ago
  Which is strange. It should be possible to implement proper CML-style concurrency in Haskell, which is strictly more expressive than the go concurrency model.

speps 9y ago

I only started Haskell since the 1st day of Advent of Code this year. I didn't see that mentioned much either in the article or other articles, but Haskell is like Python and has significant whitespace to determine scope. The error messages related to this aren't always clear...

Tehnix 9y ago
The error messages should have improved a bit with GHC 8.2[0], you might wanna check that out if you aren't already using it. For stack that'll mean using the nightlies though (e.g. `resolver: nightly-2017-12-09`). [0] https://twitter.com/raichoo/status/825045995490795521 https://twitter.com/raichoo/status/825045995490795521

culturedsystems 9y ago

One thing this doesn't mention, which might be useful to know, is that Haskell is indentation-sensitive. For instance, those examples using "let" won't compile if the lines beginning with "let" and "in" aren't indented. I'd be interested if anyone knows of a simple guide to Haskell's indentation rules - I still find it trips me up now and then.

tome 9y ago
> I'd be interested if anyone knows of a simple guide to Haskell's indentation rules - I still find it trips me up now and then. The "simple" way I deal with it is to use Emacs and press TAB until things look right :)
Tehnix 9y ago
Re indentation, you might find these two useful https://en.wikibooks.org/wiki/Haskell/Indentation https://en.wikibooks.org/wiki/Haskell/Indentation and http://echo.rsmw.net/n00bfaq.html http://echo.rsmw.net/n00bfaq.html.
- kkmx 9y ago
  That helped thanks!
masklinn 9y ago
> Haskell is indentation-sensitive. That's not really true, at least not in the way Python is. Haskell is actually defined using "braceful" syntax, and that syntax can be used anywhere (and is useful for code generation); on top of that it has Layout Rules[0]. Basically: Any time a "where", "let", "do" or "of" keyword is not followed by a brace, an implicit one is inserted and the indentation of the next lexeme (non-comment non-whitespace item) is noted[1] For any subsequent line, * if it's indented by the same amount as the one noted, a semi-colon is prepended * if it's indented by less than the noted amount, a closing brace is prepended A closing brace is also inserted when encountering an illegal lexeme (for the current structure) where a a closing brace would be legal. [0] https://www.haskell.org/onlinereport/haskell2010/haskellch2.html#x7-210002.7 https://www.haskell.org/onlinereport/haskell2010/haskellch2.... [1] except if the indentation of the next non-whitespace lexeme is less than the current indentation level, then an empty block is inserted, and layout processing for the current scope continues

mark_l_watson 9y ago

Nice guide for learning to read Haskell code! You have one minor type: "tree1123 :: IntTree tree ="

gilmi 9y ago
thanks! fixed.

hellofunk 9y ago

I once downloaded a python script, ran it with some input, and got a result. Curious, I opened the script in Emacs, which then opened it into python mode. As is my habit, I indented the whole file, which did basic white space changes to it according to python mode. I didn't realize I did this at first, and I saved and exited the script, then played around with it some more. Still got results, everything seemed the same. But when I tried it with the same input as originally, it was a different return result. This took a while to figure out, until I realized that emacs changed the indentation of just one line, because the author had apparently not followed the typical idioms or conventions of indenting python in some way. That merely opening, beautifying, and saving a file could change program output with no errors has turned me off of white space sensitive syntax ever since. Which is partly why OCaml gets some bias from me over Haskell.

mlevental 9y ago
honestly it's bananas. I can't for the life of understand how such a poor form over function decision was ever made by an engineer. the number of bugs (>0) this introduces into production code every year is reason enough (imho the only relevant metric) to prefer braces. are block delimiting braces really that onerous???
- coldtea 9y ago
  Because braces don't introduce bugs? You can just as easily omit braces in a if/for etc statement and have a bug, or close the wrong brace at the wrong point (and also introduce a bug).
  - mlevental 9y ago
    >omit braces so you're saying braceless ifs and fors are bad? yes I agree. > close the wrong brace -/+ 1 flipping the right number of braces to get that kind of bug is much much harder than indenting a block incorrectly
    - avmich 9y ago

_0ffh 9y ago

This site breaks the zoom function in Firefox. Please be considerate towards the visually impaired, and don't break zoom on one of the few browsers that actually even have a somewhat useful zoom function!

quadrangle 9y ago
While I agree STRONGLY, I just tested after seeing your comment and it led me to try the Reader mode in FF which worked perfectly and thus allows full zooming of this site.
- _0ffh 9y ago
  Wow, thank you for introducing me to that feature!
sridca 9y ago
It doesn’t even work on iOS safari.
- gilmi 9y ago
  You can view this as markdown on github[0] [0]: https://github.com/soupi/rfc/blob/master/reading_haskell.md https://github.com/soupi/rfc/blob/master/reading_haskell.md
gilmi 9y ago
I'm sorry for that. I'll try to fix this when I can. For now you can view the markdown document instead of the slides here: https://github.com/soupi/rfc/blob/master/reading_haskell.md https://github.com/soupi/rfc/blob/master/reading_haskell.md

bachmeier 9y ago

Haskell is one of the few major languages I haven't used much. I find this to be very helpful. Sometimes I look at the Pandoc source and wonder what the hell I'm looking at.

swlkr 9y ago

I've always been confused when reading Haskell snippets on the web, this really cleared things up for me!

cygned 9y ago

x +- y = (x + x) - (y + y) That's crazy. I should learn Haskell (again).

mlevental 9y ago
what exactly is crazy about this?
- runeks 9y ago
  The simplicity with which a new operator is defined.
  - cygned 9y ago
    This. Incredible elegant. I always enjoy these types of things when programming Lisp.
  - akhilcacharya 9y ago
    I think this is a downside. It just makes reading new code that uses esoteric symbols defined elsewhere.
    - gilmi 9y ago
      This[0] operator glossary reviews the most used operators. [0]: https://haskell-lang.org/tutorial/operators https://haskell-lang.org/tutorial/operators
Tehnix 9y ago
`+-` here is an entirely new operator though. The shuffling of arguments might look a bit weird though, it could also be written (+-) x y = (x + x) - (y + y) Symbol operators are automatically infix though, and you can make them normal using (), same as backticks make normal functions infix, `a la 2 `plus` 3.

notsgnik 9y ago

nice guide

weavie 9y ago

Haskell can be very readable and elegant, but what I do find frustrating is when research papers show sample Haskell, but it's not quite Haskell. They just can't seem to resist the urge to replace various operators and types with their own non-alphanumeric symbols, thus making what should be reading simple code into some kind of hieroglyphic translation exercise..

leshow 9y ago
There are a bunch build into the language, I think a lot of libraries take their queue from there. Still, after you get over the initial hurdle of like <$> == fmap. It's not so bad.
nybble41 9y ago
> when research papers show sample Haskell, but it's not quite Haskell For the most part the code in the research papers actually _is_ valid Haskell, provided you enable the -XUnicodeSyntax extension and include a few extra modules. Haskell 98 permits Unicode symbols and identifiers; the extension covers the handful of symbols which are built in to the language or enabled by other extensions. You can find a full list here: https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/glasgow_exts.html#unicode-syntax https://downloads.haskell.org/~ghc/latest/docs/html/users_gu... Personally I prefer Unicode symbols and tend to use them whenever possible. I have some XCompose rules configured to make them easier to type. Unfortunately, I have yet to find a comparable input system for Windows.

nigwil_ 9y ago

I like the content but: I can't link to the slide because of the way these pages are defined: slide 11: The presented argument order in the ASCII-art of Red, Blue, Green I think should be Red, Green, Blue to match the usual initialism. I could not find a way to submit a pull-request for this presentation, and my search-fu on github failed to find the associated repo, and there were no links I could find in the presentation to submit comments.

gilmi 9y ago
Thanks! fixed. You can find the document and repo here: https://github.com/soupi/rfc/blob/master/reading_haskell.md https://github.com/soupi/rfc/blob/master/reading_haskell.md