GHC 7.8.1 released

http://www.haskell.org/pipermail/haskell/2014-April/024137.html

by ocharles • 12 years ago

249 101 12 years ago

haskell.org

Osmium• 12 years ago

I'm intrigued by "full iOS support." Does this mean it's now possible to write iOS apps using a Haskell backend?

SmileyKeith• 12 years ago

Assuming it has something to do with this[0] but I'd be interested to know as well.

[0] https://ghc.haskell.org/trac/ghc/wiki/Building/CrossCompilin...

sigzero• 12 years ago

"In particular, GHC now has all the necessary patches to support cross compilation to Apple iOS, using the LLVM backend."

efnx2• 12 years ago

Yes - you can now compile Haskell code to run on iOS. There are still a few unusual steps that involve ffi but its pretty easy to get a trivial project up and running. I have an unfinished project that shows the process. https://github.com/schell/blocks

carterschonwald6• 12 years ago

Yes. Everything but certain naive use of template Haskell or use of ghci is supported for targeting IOS. There's also some related engineering to provide android support

icetortoise• 12 years ago

While this is nice, it results in a big static lib(27M) to include in your app. This might be okey for some games, but maybe not for small apps. I was very interested in a Haskell app, but eventually gave up because of this...

maxpow4h• 12 years ago

the twitter app is 30M, we have already past the point of sensible app sizes. edit: fb messenger is 60M, a ghc-ios app with the elm compiler baked in is 24M.

thinkpad202• 12 years ago

I'm also intrigued. How would one program for iOS in a practical sense with Haskell? A great deal of iOS programming, as I understand it, is navigating the APIs and libraries provided by the SDK... is this a simple task in Haskell? The FFI is something I haven't really dealt with much yet. I guess people could/will start writing wrapper libraries?

JoshTriplett3• 12 years ago

Haskell has one of the best FFIs I've ever seen; calling C code from Haskell is quite trivial, and you can write all of the necessary wrapper code and objects (such as automatic memory management or object destruction) in Haskell using common wrappers.

I'd also highly recommend c2hs for writing new wrapper libraries.

chc4• 12 years ago

I think the idea is that you would use the standard tools for the edges of the program with a Haskell core underneath handling the thinky bits. (I have no experience at all doing this, but it seems like the natural use case.)

lukexi• 12 years ago

I'll be giving a workshop on using GHC iOS at BayHac 2014 [1] along with a demo of http://tree.is which is built entirely on top of it!

[1] http://www.haskell.org/haskellwiki/BayHac2014

tree_of_item• 12 years ago

Is GHCJS easy to install now? I'm very excited about that.

carterschonwald6• 12 years ago

Luite is probably going to announce something like that in a few days. Ghcjs getting ready for general release was blocked by ghc 7.8.1 not being released.

reirob• 12 years ago

[..] http://www.haskell.org/ghc/docs/7.8.1/html/users_guide/type-... [..]

This extension allows programmers to use the list notation for construction of structures like: Set, Map, IntMap, Vector, Text and Array. The following code listing gives a few examples:

['0' .. '9'] :: Set Char

[1 .. 10] :: Vector Int

[("default",0), (k1,v1)] :: Map String Int

['a' .. 'z'] :: Text

http://www.haskell.org/ghc/docs/7.8.1/html/users_guide/type-...

tel6• 12 years ago

Woah! I did not know that was going to be included! Here's to hoping it makes as much a splash as OverloadedStrings did!

IsTom2• 12 years ago

As a non-fan of OverloadedStrings, I'm not sure how I feel about this.

carterschonwald6• 12 years ago

For those who write large scale applications, web or otherwise, the mio io manager improvements should be especially exciting. See http://www.reddit.com/r/haskell/comments/1k6fsl/mio_a_highpe... for a prior discussion.

hamidr• 12 years ago

I was reading the paper and got stuck somewhere when I saw this:

With Mio, realistic HTTP servers in Haskell scale to 20 CPU cores, achieving peak performance up to factor of 6.5x compared to the same servers using previous versions of GHC. The latency of Haskell servers is also improved: <snip> under a moderate load, reduces expected response time by 5.7x when compared with previous versions of GHC
Available with GHC 7.8.1

Nice job.

carterschonwald6• 12 years ago

One really cute feature that some systems folks might like is there's now support for calling the CPU/hardware prefetch instruction where applicable. http://www.haskell.org/ghc/docs/7.8.1/html/libraries/ghc-pri...

sanxiyn• 12 years ago

Even better, if you use vector library, prefetch instructions are automatically (and nearly optimally) inserted for your loops written in higher-order functions like fold.

Details here: http://research.microsoft.com/en-us/um/people/simonpj/papers...

carterschonwald6• 12 years ago

Nope. That's not in the release version. Simd is still second class in ghc. Should be viable for ghc 7.10 though. Note well, the prefetches in that paper aren't optimal. In many cases prefetch is over issued.

You should only use prefetch when benchmarks show that the hardware prefetch isn't performing up to sniff. Or when your access pattern for data doesn't have good locality and doesn't resemble a linear arithmetic sequence. (Just rules of thumbs mind you. For more precise heuristics, please read your CPU vendors optimization manual. The intel manual has quite a few tricks that should apply to most modern CPUs overall)

masida2• 12 years ago

What will be the easiest way to get GHC 7.8.1 running alongside the official GHC packages for Debian (specifically Jessie)?

Should I download a package from http://deb.haskell.org/? If so, where can I find 7.8.1?

carterschonwald6• 12 years ago

That is maintained by an active ghc contributor, so should be safe to use!

JoshTriplett3• 12 years ago

GHC 7.8 is already packaged in Debian experimental, so if you're running current testing, you may find it easiest to just add sources for experimental and sid, set the default release to testing (so you don't upgrade anything else), and then install GHC 7.8 directly. You'll end up upgrading a pile of Haskell packages to versions from experimental, but mostly not the rest of your system.

thoughtpolice3• 12 years ago

You can use these PPAs from our friend, Herbert: https://launchpad.net/~hvr/+archive/ghc/

They are packaged for Ubuntu, technically (12.04 Precise) but you can just add the apt-repository line to your `sources.list` and it will work fine, and plenty of people are doing this.

A repository for the STABLE branch will eventually appear on http://deb.haskell.org, but I'm not sure when Joachim will do this.

jberryman• 12 years ago

The binary distributions install alongside your system packages or other bindists quite nicely (they might overwrite the /usr/bin/ghc symlink, but that's it) and you can select which ghc version you want to use when using cabal with the `-w` flag. Each will keep a separate package db, etc. So be bold!

masida2• 12 years ago

Thank you for your comment. I've ended up installing 7.8.1 from the binary distributions from the GHC site: http://www.haskell.org/ghc/download_ghc_7_8_1

As easy as:

  tar -xJvf ghc-7.8.1-i386-unknown-linux-deb7.tar.xz
  cd ghc-7.8.1
  ./configure --prefix=/opt/ghc-7.8.1
  make install

swift• 12 years ago

I don't recall ever being excited about a compiler release before, but this has got me excited. Typed holes, overloaded lists, pattern synonyms, new IO manager, new code generator, interruptible FFI calls, parallel compilation, and tons of other new features.

One thing I'm particularly excited about is the switch to use the system's dynamic linker instead of a custom one in GHCi. The custom linker GHCi used before didn't support some features used by C++ code, which meant that some of my FFI-based projects weren't usable in GHCi. This also affected other things that used a GHCi-like code path like Template Haskell and the GHC APIs used by ghc-mod/hdevtools. This will be huge for usability for me when working on projects that link to C++.

Hat tip to all the GHC developers for a truly amazing release!

thoughtpolice3• 12 years ago

The dynamic switch isn't without its pain points. In particular, the way we currently implement it leaves some things to be desired, and it's lead to some other rather unfortunate ramifications for Windows right now.

Truthfully, me and Simon now have reservations about if this is the right way to go, and we should instead invest more infrastructure into our own Linker (which, independently, got some nice bug fixes this time around - constructors and weak pointers now work, for example.) ELF support is quite complete (and very stable) for example. It's just a question of what's the most work.

ciferkey• 12 years ago

Great! Can't wait until the next release of the Haskell Platform now.

chowells4• 12 years ago

Don't.

There's no benefit to handcuffing yourself to the platform. Just install ghc and cabal, and enjoy yourself.

lomnakkus• 12 years ago

... and use cabal sandboxes! Otherwise the "enjoy yourself" bit may be a little short-lived ;)

Sir_Cmpwn• 12 years ago

I really want to get into Haskell, but I just don't understand it. The tutorial on the official site doesn't do it for me. Can anyone suggest alternative resources for learning? I'm used to C-like languages.

Thanks for all the responses. I'll start with LYAH.

bretthoerner• 12 years ago

http://learnyouahaskell.com/chapters

Dewie• 12 years ago

Learn You A Haskell For Great Good (free online book) is the most common recommendation for beginners.

gamegoblin• 12 years ago

I tried getting into haskell probably 3 times before it really stuck with me. After getting over the initial hump it's heavenly. I started with LYAH like others have recommended. Persistence!

dmunoz• 12 years ago

Learn You a Haskell for Great Good! has already been recommended, which I would have said if it had not yet been.

There is also Real World Haskell [0]. It's a lot less long winded than LYaH, which is good or bad depending on how you like to digest information.

Also, check out FP Complete's FP Haskell Center [1]. It contains community written tutorials with inline runnable code examples, so you can really get a feel for Haskell by manipulating and playing with the examples right on the site.

[0] http://book.realworldhaskell.org/read/

[1] https://www.fpcomplete.com/business/fp-haskell-center/

RaphiePS• 12 years ago

I'm a big fan of http://learnyouahaskell.com/

tel6• 12 years ago

Others have linked tutorials. I'm going to leave some advice: pretend like you're learning to program from scratch. Not just mentally but in how you invest. It will likely take some amount of time, it will likely happen in stages of progressively receding complete astonishment and confusion, and you will be served to be proud of silly things like getting simple programs to even compile.

Sounds kind of miserable, right?

That's why you should also prepare for it with some of that early curiosity and wonder that drove us all to learn programming to begin with.

Haskell is probably unlike anything you've used before.

freyrs3• 12 years ago

This is most certainly the best advice you can give to someone coming from other languages. I constantly see people I very much respect for their skills in other programming disciplines get very angry and make otherwise irrational rants about Haskell because they can't translate their hard won skills over to this new model. Learning Haskell will make one feel like a beginner again, should just embrace that from the start.

efnx2• 12 years ago

After LYAH I learned a lot from doing as many of the 99problems set for Haskell as possible.

http://www.haskell.org/haskellwiki/H-99:_Ninety-Nine_Haskell...

dengnan• 12 years ago

When I learn something, I would like to simultaneously read several books on the same topic, so that I could learn same things from different perspective. It works great for me when I learn Haskell, Scala, and other things.

Here is the list of materials I used to learn Haskell:

1. LYAH, http://learnyouahaskell.com/

2. Real world Haskell: http://book.realworldhaskell.org/read/

3. Programming in Haskell: http://www.amazon.com/Programming-Haskell-Graham-Hutton/dp/0... (No one suggests this book, but I do think this book is well-written and concise.)

4. Video tutorial by Erik Meijer based on Programming in Haskell: http://channel9.msdn.com/Series/C9-Lectures-Erik-Meijer-Func...

5. Advanced topics: http://www.haskellforall.com/2014/03/introductions-to-advanc...

Edit: Format

embwbam• 12 years ago

One thing to keep in mind: Haskell is different enough that it's almost as hard as learning to program the first time.

To learn something that hard, you need to be exposed to it multiple times. You'll probably get overwhelmed even with LYAH, but give it some time and come back to it.

lelf• 12 years ago

I can recommend reading SICP first if you know nothing about functional programming. It will likely help a lot. And forget everything you know from C-like languages (I'm not joking).

Buttons840• 12 years ago

I recommend the 99 Haskel problems: http://www.haskell.org/haskellwiki/H-99:_Ninety-Nine_Haskell...

All questions have solutions you can learn from; most have multiple solutions. I have learned a lot from doing these problems and doing additional research where needed.

(This is in addition to the other good learning resources like the oft mentioned LYAH.)

SkyMarshal• 12 years ago

Miran Lipovaca's LYAH is one of the best intro to programming, not just intro to Haskell, books I've read. He's great at explaining complicated technical concepts clearly.

nnq• 12 years ago

I sincerely recommend against LYAH! It takes sooooooooo loooooong to get to the interesting bits that actually make Haskell worth learning an has so many try-to-be-funny examples that it makes you run away screaming... I tried going through it but it was literally oscillating between putting my mind to sleep and making wish to grab a chainsaw :) And the "humor" and "pretty pictures" don't help either... they were more like poignant guide to ruby, something that you either love or they annoy the hel out of you (this was for me), but either way they don't help the learning experience at all.

I suggest HFH ("Haskell Fast & Hard") as the introductory tutorial to start with instead. You can pick from 2 formats:

- http://yannesposito.com/Scratch/en/blog/Haskell-the-Hard-Way... - static all-in-one-page format with pretty pictures

- https://www.fpcomplete.com/school/to-infinity-and-beyond/pic... - split version, but with the ability to open snippets in their web based IDE

...after this, Real World Haskell is probably the next step: http://book.realworldhaskell.org/read/ (I'm still at this step).

rando289• 12 years ago

I accidentally upvoted you, but I disagree. LYAH is a great book to actually read through, and I enjoyed the humor. real world haskell introduces things without explaining and it's quite confusing and inconsistent.

virtualwhys• 12 years ago

I concur, LYAH was, for me, not a terribly useful intro to Haskell.

Running through some chapters of Real World Haskell online, however, is proving to be a bit of an eye opener ;-)

Might just be that I could care less about hand drawn illustrations and the occassional somewhat humerous aside.

YMMV, many seem to love LYAH.

tavoe• 12 years ago

To me, the core of Haskell is that: "Haskell is C with one semi-colon per function."

This forces you to put all your code into method signatures. This, in turn, means Haskell (or C, if you follow the 1 semicolon rule in C) can understand almost everything about your program.

If you actually follow the 1 semicolon rule in C, you'll get very verbose syntax. All of Haskell's syntax is in service of making programming in this style palatable.

coolsunglasses2• 12 years ago

If you want an alternative opinion from somebody who

1. Has taught a lot of Haskell

2. Thinks LYAH is better as a reference than a step-by-step method for learning Haskell

Then see my Learning Haskell gist here (it includes Haskell Fast & Hard, and other things too).

https://gist.github.com/bitemyapp/8739525

If anybody is learning Haskell and needs help, please email me.

Edit: I agree with nnq, I think LYAH moves too slowly and fails to show you what about Haskell is truly different and worthwhile in a compact enough format. That said, it is great as a reference as the explanations of concepts are stand-alone. (unlike RWH which is more project-oriented)

Edit2: You are going to feel a bit lost after Haskell Fast & Hard. This is natural. That's why I have you do the NICTA course. It firms things up.

Edit3: I think RWH is a great reference as well, but the mid-to-late chapters have a bit of an "in media res" thing going on because there are projects being walked through cross-chapter. That said, it has a very nice and simple example of, "pre-monads, ugly code; post-monads, pretty code". RWH also covers topics that you'll care about if you're doing Haskell in production.

mitchty• 12 years ago

Cool, i'm going to look at that gist for this years "try to learn haskell... again" attempt. :)

I do it every year but hit io monads and my mind continually just has a core dump. Some year I hope to climb everest.

dllthomas6• 12 years ago

No one's mentioned the wikibook. I've not read through it much, but a colleague found it far more readable than LYAH: http://en.wikibooks.org/wiki/Haskell (I loved LYAH myself, though, so YMWillProbablyV).

Also, there's no substitute for talking to people. Hop on the Haskell Beginners mailing list (http://www.haskell.org/mailman/listinfo/beginners) or drop by the IRC channel (#haskell on freenode), where people couldn't be friendlier.

joehillen• 12 years ago

Don't bother with LYAH. I learned Haskell from a lecture created by one of the creators of the language, Philip Wadler: https://www.youtube.com/playlist?list=PL4C1D41CB47EED318

TazeTSchnitzel• 12 years ago

I'm enjoying Learn You a Haskell.

Then again, that might be because when I looked into Haskell, I realised it was the language I wished to create.

startling2• 12 years ago

(hi!)

You might like this:

http://www.haskell.org/haskellwiki/Haskell_Tutorial_for_C_Pr...

And the Gentle Introduction is not very gentle but is a good reference:

http://www.haskell.org/tutorial/

stusmith1977• 12 years ago

I've found the "24 Days of Hackage" series incredibly useful - each day is a brief introduction to a useful Haskell library, many of which show off features of Haskell that aren't available in 'standard' languages. Even better, each one comes with working example source on GitHub, so you've got a starting point if you do want to experiment.

http://ocharles.org.uk/blog/

(I'm a Haskell beginner, currently experimenting with using Scotty, Persistent and Esqueleto to make a web API - and these articles have been so useful to me - I'm finally getting my head around monad transformers, using them to extend the standard Scotty one. Proud moment for me.)

rasur• 12 years ago

I'm lurching through the wikibook: http://en.wikibooks.org/wiki/Write_Yourself_a_Scheme_in_48_H... with a side order of the Haskell Report/Reference for when things are not clear to me.

Both are helping my limited experience of Haskell greatly.

izietto• 12 years ago

I want to find a job as Haskell programmer!

dllthomas6• 12 years ago

I've projects I'd be willing to delegate, if I can pay you sufficiently little...

jc79• 12 years ago

Sharing izietto's wish, how might one contact you?

dbbolton• 12 years ago

A bit off topic- why is GHC so large? I recently noticed it was over three times the size of gcc (for amd64, in an .xz archive).

thinkpad202• 12 years ago

This might be interesting to you: http://stackoverflow.com/questions/4858585/why-is-ghc-so-lar...

jeorgun• 12 years ago

Now I'm kind of curious. The GHC is listed there as being 113 megabytes. When I try to install it on Arch Linux, the size is listed as 736MB! What in God's name is Arch doing to nearly septuple the size of this package— and more to the point, does anyone know any way of getting it to not do that? I'd very much like to learn Haskell, but taking up that much space on my laptop's SSD is a dealbreaker.

elwell• 12 years ago

Short answer: GHC is not just a compiler; it's also a rather large library.

Avalaxy• 12 years ago

This is great news for all 5 haskell programmers!

Just kidding, Haskell is a great language, it's unfortunate that the tooling is still way behind (at least on Windows) and that it isn't used much.

BSousa• 12 years ago

I know enough about Haskell to be excited, but recently, I implemented a few systems with F# and am really happy with the language. If we forget about the .net/MS thing (and all the hatred that comes from that), are there real true advantages of going Haskell for a greenfield project over F# ? (I have a couple heavy algorithm heavy Haskell projects done, but having worked with F# more and more, I feel like it is so much nicer as a modern, not bend over your back to deal with the purity/lazy aspects language than Haskell).

chowells4• 12 years ago

I've been playing around with the new PatternSynonyms extension. In combination with the existing ViewPatterns extension, I'm going to really have to change the way I think about API design. This is actually pretty fantastic.

    {-# LANGUAGE ViewPatterns, PatternSynonyms #-}
    
    import Data.Set as S
    
    -- patterns that a library might provide
    pattern x :< m <- (minView -> Just (x, m))
    pattern m :> x <- (maxView -> Just (x, m))
    pattern Null   <- (S.null  -> True)
    
    -- a really dumb test function using those patterns
    doubleMin :: (Ord a, Num a) => Set a -> Set a
    doubleMin (x :< s) = insert (2 * x) s
    doubleMin x = x

Ignore how dumb my test function is, and just focus on how lightweight it becomes to match views of the data structure. Figuring out what patterns to include my libraries is going to be a fun new design point.

axman6• 12 years ago

I haven't had a look at the extension definition itself, but I find this really hard to read. Can you or someone else give an explanation of what's going on? It seems to me that the brackets are all wrong, I would've expected

    pattern (x :< m <- minView) -> Just (x,m)

but that's just basically view patterns/pattern guards. Basically I can sort of see what's going on here, but only in this specific case; I can't see how one uses this elsewhere.

chowells4• 12 years ago

The choice of character for unidirectional patterns isn't the greatest, I'll agree.

The PatternSynonyms extension enables two new top-level declarations, both declared with "pattern".

    pattern NestedJust x = Just (Just x)
    pattern NestedNothing = Just Nothing

That's the easier syntax of a bidirectional pattern synonym. They can be used both as patterns and as expressions.

    foo :: Maybe (Maybe Int) -> Bool
    foo (NestedJust 7)  = True
    foo (NestedNothing) = False
    foo _               = False

    bar :: Maybe (Maybe String)
    bar = NestedJust "hello"

There are a couple terrible examples. Bidirectional pattern synonyms must be valid as both expressions and pattern matches, or you get a compile error

My example was using unidirectional pattern synonyms. They allow any pattern match whatsoever as the body; the expression restriction is dropped because they aren't allowed to be used in expression contexts. They are defined using <- instead of =.

    pattern MinView x m <- (minView -> Just (x, m))

That's functionally the same as the :< example above, but possibly a bit simpler to read, because the precedence of the symbols is more obvious. It defines a pattern synonym named MinView that is translated to the view pattern in parens.

It's quite possible you were conflating view pattern syntax with pattern guard syntax as the source of your confusion.

GHC 7.8.1 released

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