In the Haskell docs here http://www.haskell.org/haskellwiki/Debugging it mentions Hat to do offline debug traces, but that page is online. I found it via Google but it seems outdated; what is the best way to do offline Haskell traces?
Hat isn't outdated -- olaf chitil revived it and is actively maintaining it: http://olafchitil.github.com/hat/
The latest version on hackage is tested to build with ghc 7.6.
It does, however, still only work on Haskell 98, with a few extensions. So programs that use more advanced GHC extensions (particularly regarding fancy type tricks) won't work with it. To my knowledge, there's nothing similar to hat that's been extended to handle a wider range of extensions to Haskell.
Related
Long story short, I'd like some guidance on what's the (best) way to have Haskell work on Archlinux.
By work I mean all, in terms of the ghci command line tool, installing packages I don't have - such as vector-space, which this answer to a question of mine refers to -, and any other thing that could be necessary to a Haskell obstinate learner.
Archlinux wikipage on Haskell lists three (alternative?) packages for making Haskell work on the system, namely ghc, cabal-install, and stack. I have the first and the third installed on my system, but I think I must have installed the latter later (unless it's a dependency to ghc) while tampering around (probably in relation to Vim as a Haskell IDE). Furthermore, I have a huge amount of haskell-* packages installed (why? Who knows? As a learner I must have come multiple times to the point of say uh, let's try this!).
Are there any pros and cons ("cons", ahah) about each of those packages?
Can they all be used with/without conflicts?
Does any of them make any other superfluous?
Is there anything else I should be aware of which I seem apparently ignorant about based of what I've written?
Arch Linux's choice of providing dynamically linked libraries in their packages tends to get in the way if you are looking to develop Haskell code. As an Arch user myself, my default advice would be to not use Arch's Haskell packages at all, and instead to install whatever you need through ghcup or Stack, starting from the guidance in their respective project pages.
You are basically there. Try the following:
ghci: If you get the Haskell REPL then it works.
stack ghci: Again you should get the Haskell REPL. There are a lot of versions of GHC, and stack manages these along with the libraries. Whenever you use a new version of GHC stack will download it and create a local installation for you.
stack is independent of your Linux package manager. The trouble is that your distro will only have the Haskell libraries it actually needs for any applications it has integrated, and once you step outside of those you are in dependency hell with no support. So I recommend that you avoid your distro Haskell packages. stack does everything you need.
If you installed stack from your Linux package manager then you might want to uninstall it and use a personal copy (i.e. in your ~/.local directory) instead. Then you can always say stack update to check you have the latest version.
Once you have stack going, create a project by saying stack new my-project simple. Then go into the project folder and start editing. You can work with just a .hs file and GHC if you really want, but its painful; you will do much better with stack, even if you are just messing around.
You'll also need an editor. Basic functionality like syntax highlighting is available in pretty much everything, but once you get past Towers of Hanoi you are going to want something better. I use Atom with ide-haskell-ghcide. This uses the Haskell Language Server under the hood, so you will need to install that too. I know a bunch of other editors have HLS support, but I don't have experience with them.
I want to write a Haskell function (module) of type: String -> String to call in Android. The easiest method seems to use JHC to generate C code, then use Android NDK to generate a shared library, but I could not find any documentation for JHC. Does JHC also use Cabal to build? Is JHC stable enough to use Parsec or Attoparsec library?
Back in 2011 I had limited success using JHC in a similar way, but targeting iOS instead of Android. Initial results were good in just getting the thing running, but we ended up discarding JHC in favor of GHC precisely because we started getting weird compile-time errors on programs that used Parsec. Bear in mind, this was in 2011 so JHC might have improved by a lot since.
If you want to give GHC a chance, I'd recommend looking at this example which uses GHC 7.8 to compile a game for Android. I haven't used it in anger yet, but I did manage to get it working on Docker, getting as far as rebuilding the game from scratch and installing it on a real Android device, so the approach definitely has merit.
UPDATE as of August 2017: Moritz Angermann has posted detailed instructions on targeting Android with a GHC cross-compiler.
Well a compiler called eta maybe the most convenient way now.it targets jvm and it will produce a jar file so you can directly put it in your project
I'm about to get into Haskell, and I'm a bit confused why I'm recommended to install both GHC and the Haskell-platform via brew.
Isn't GHC a Haskell implementation/compiler?
When does one need the platform?
Short answer:
The Haskell Platform is a collection of stuff.
GHC is one specific component of those stuff.
Longer answer:
Usually you want to install the Haskell Platform, because then you get lots of stuff installed all in one go as opposed to having to manually set up all the pieces one at a time.
That's the purpose of the Haskell Platform.
To give some historical perspective: before the Haskell Platform was invented, GHC itself used to come with a random grab-bag of libraries.
The Haskell Platform was invented so that somebody less overworked could decide which libraries should and shouldn't be included out of the box (i.e. so the GHC people could stop thinking about libraries and go back to thinking about GHC).
It's been quite successful in that respect.
The Haskell Platform is a collection of compilers, tools and libraries for Haskell.
It currently specifies that GHC is included in the platform.
Compliant Haskell Platform packages will install GHC without additional work required on the part of the user.
I have the Haskell Platform 2012.4 installed on Windows. I would like to try the new extensions in GHC 7.6.2. It looks like the GHC 7.6.2 x86_64 download does not include an installer and is just the binaries. What is the proper way to get the latest version installed and set as the default for building Haskell projects? Thanks.
If you download GHC itself, you just get GHC and a tiny handful of libraries. If you download the Haskell Platform, you get GHC plus a much bigger collection of libraries. However, the Haskell Platform is updated infrequently, so you'll get an older version of GHC.
If you're asking "how do I install the Haskell Platform and then make it work with a newer GHC?", then the answer is "you don't". Haskell libraries have to be compiled for the specific version of GHC you're using.
You basically have two options:
Use the Haskell Platform, together with the version of GHC that it supplies.
Use the latest GHC, and compile whatever libraries you want manually.
On Linux it's not too bad, but Haskell libraries that bind to external C code tend to be fiddly to build on Windows. (Stuff like OpenGL, zlib, etc.) Packages that are 100% vanilla Haskell code are drop-dead easy to compile on any system.
I haven't done this and I'm at work so I can't test it out, but looking at the GHC docs I would think you can use the --with-compiler=path flag to select which version of GHC to use?
See also this question, related to using cabal with multiple versions of ghc installed. I would guess that you probably want to use cabal-dev or something to sandbox this, otherwise your package database may become a mess.
EDIT: As far as a default, I think you can set that in a cabal configuration file. See the comments to the accepted answer in that question I linked.
The other answers here are great, and I wanted to add that the current best way to get the latest version of GHC installed is to look at haskell.org's installation instructions. I bounced between lots of different options before I landed there, and I think it's the best source of truth from what I can tell.
To summarize the current instructions: if you already have chocolately set up, "at an elevated command prompt, run choco install haskell-dev, followed by refreshenv."
In Common Lisp, programs are often produced as binaries with a translator bundled inside. StumpWM is a good example.
How would one do the same with Haskell and OCaml?
It is not necessary to provide a debugger as well, as Common Lisp does, the aim is to make extensions while not depending on the whole translator package ( xmonad which requires GHC ).
P.S. I know about ocamlmktop, and it works great, except I don't really get why it requires "pervasives.cmi" and doesn't bundle it with the binary. So, best thing I can do is mycustomtoplevel -I /path/to/dir/with/pervasives.cmi/. Any way to override it?
This isn't really possible for (GHC) Haskell - you would either need to to ship the application binary + GHC so you can extend via GHC-API, or embed an extension language. I don't think there are any "off-the-shelf" extension languages to embed in Haskell at the moment, though HsLua might be close. This is a bridge to the the standard (C source) Lua. There was a thread on Haskell-cafe last month about extension languages written in Haskell, I think the answer was 'there aren't any'.
http://www.haskell.org/pipermail/haskell-cafe/2010-November/085830.html
With GHC, there is GHC-API, which allows you to embed ghci-like interpreters in your program. It's a quite low-level and often changing library, since it simply provides access to GHC internas.
Then, there is Hint, a library which aims to encapsulate ghc-api behind a well designed and more stable interface.
Nevertheless, I've recently switched from using either of these packages to using an external ghci. The external ghci process is controlled via standard input/output pipes. This change made it easy to stay compatible with GHC 6.12.x and 7.0.x, while our ghc-api code broke with GHC 7.x and hint didn't work out of the box either. I don't know whether there is a new version of hint available, which works with GHC 7.
For Ocaml, have you tried using findlib? See the section Custom Toploops.