I am trying to run the Haskell script in this StackOverflow answer. Pandoc appears to execute the runhaskell executable because I get the error
Could not find executable runhaskell
Seems like I need Haskell. So I google "install haskell", go to haskell.org, and follow the install instructions. It appears to install correctly. For example, I now have a $HOME/.ghcup/ directory and the stack command works. However, runhaskell still does not work. When I search Haskell Tool Stack, I don't see any meaningful hits. However, there is a stack command called runhaskell. When I add stack runhaskell to the top of chapter.hs from the previous post, I get the same error.
I even tried following a "hello world" for Haskell but the first step, using ghci, fails. So maybe I didn't even install the Haskell Platform correctly.
Feels like a really stupid issue, but I can't figure out how to install the executable runhaskell which, I assume, will run a Haskell program.
looks like runhaskell is not in your $PATH
Related
I code haskell of poor quality in december each year. This year my environment is broken for some reason.
When I try to run my old scripts with
runhaskell .\myCode.hs
I get
Could not find module `Data.List.Split'
Use -v to see a list of the files searched for.
This question has a comment in one of the answers:
Maybe he doesn't even use a .cabal or .yaml file and only wants to write a stand-alone Haskell script for runhaskell.
That is exactly what I'm after, but the comment thread does not provide an answer. It worked 2016-2018 and I do not remember this issue, and I've never had the setup that is written about here or here("hidden modules").
Anyone have an idea how to fix this?
Edit: I tried the guide here which says to download the package, extract it and run:
runhaskell Setup configure
runhaskell Setup build
runhaskell Setup install
But I just get an error which says:
$ runhaskell Setup configure
Configuring split-0.2.3.3...
Setup: Encountered missing dependencies:
base <4.12
And I do have a Haskell\8.6.3\lib\base-4.12.0.0 in the installation.
Data.List.Split is not part of "base", the core libraries that are distributed with Haskell. It is part of an external package named "split". If you want to use it, you must get that package somehow. This is typically done with cabal or stack. Perhaps there is a way to do this that runhaskell understands; I don't know anything about runhaskell.
Ok so after following the instructions to do things manually, I double checked that I had the latest split package. The web page says the package requires base (<4.14) but it still complains Setup: Encountered missing dependencies: base <4.12 when I try to run runhaskell Setup configure
But then after I've tried and failed to install an older 'base', seemed like a long shot anyway, I simply followed the 'Installing packages using cabal' part of the guide.
cabal update
cabal install split
I ran those two commands and ignored the warnings that it was part of the legacy v1 cabal usage. It worked and it installed split so the runhaskell command could access it.
I am reading "Learn you a Haskell for great good", and have reached the chapter on I/O actions. I am using Windows, and have downloaded GHCi and WinGHCi.
I'm trying to compile a simple program and have saved a file on emacs as helloworld.hs with main = putStrLn "hello, world" in it.
The book says
Open your terminal, navigate to the directory where helloworld.hs is located, and enter the following:
$ ghc --make helloworld
However, if I enter $ ghc --make helloworld onto GHCi and WinGHCi I receive errors such as the one below, perhaps because I need to enter $ ghc --make helloworld elsewhere:
<interactive>:7:1: error:
parse error on input ‘$’
Perhaps you intended to use TemplateHaskell
In fact, in the online edition of the book (here: http://learnyouahaskell.com/input-and-output), the author remarks that:
For the purposes of this chapter, I'm going to assume you're using a unix-y environment for learning Haskell. If you're in Windows, I'd suggest you download Cygwin, which is a Linux-like environment for Windows, A.K.A. just what you need.
Question 1: Is it necessary for me to download Cygwin, or some other such thing, in order to be able to compile the program by entering $ ghc --make helloworld?
I ask this, since if there were some other way of compiling the program it would be very useful to know, since I am on a university computer and cannot download things like Cygwin without permission. (and even with permission it might not be possible, depending on what Cygwin requires)
Question 2: Given that only the technicians of my university are away for Easter, and only they can download things on this computer, how can I proceed with the chapter in I/O actions? Is it possible just to continue, but ignore the sections involving compiling programs?
In many Unix and Linux shells (at least in Bash with which I'm most familiar) the default prompt is $. That's what the shell displays.
On Windows, when you open a Command Prompt, you'll typically see something like this instead:
C:\Users\mark>
(That's my prompt.)
While instructions often include the $ prompt in order to indicate that the code is something that you're expected to enter at a command prompt, you're not expected to type the $. Just type ghc --make helloworld and hit Enter.
Also, you're not expected to do this from within GHCi, but from the command line. ghc is a command-line executable (an .exe), just like e.g. git. It has to be in your path, though, or otherwise, you'll have to type the full path the executable every time you want to run it.
You have downloaded ghci, which is interpreter. It is, by my opinion, totally enough to learn with it (it can :load sources as well), but you need to run a bit other commands. I don't know if your installation include compiler, I would not assume anything about it.
btw, you are typing command inside the interpreter already, the error message is specific for that
ps: to do same as "ghc --make" from the interpreter, run:
:load <file>
Yes, it will recurse to depenzecies automatically. You could use :help to learn other commands
I am trying to learn Haskell from the book Learn You a Haskell by Miran Lipovača. Both the book and haskell.org recommends installing the Haskell Platform but there is no download for Manjaro Linux (Arch based) which I use.
I found this guide from 2014 and decided to install the packages from Manjaro's repository. This worked fine until I wanted to use haskell-mode in Emacs. I troubleshooted this and found out that it was a problem with the packages (Stack mainly).
Looking for ways to fix this I found this Reddit thread, which describes ways to install Haskell (not the Platform), and problems with the packages. I followed one of the comments and ended up installing Stack (and GHC) with the script as described here:
wget -qO- https://get.haskellstack.org/ | sh
stack setup
stack update
My questions are related to this:
Is this the recommended starter way to install a functioning Haskell (Platform) on Linux (Manjaro) in 2018? If not: what is the/a way to do it?
Haskell Platform contains: GHC, Cabal, Stack, and some packages. GHC and Stack are installed, how do I install Cabal through Stack?
Do I need Cabal (Stack seems to have overlapping functionality)?
Looking at the packages of the Haskell Platform, what, if anything, am I missing by installing Stack as described above? Looking in $HOME/.stack/programs/x86_64-linux/ghc-tinfo6-nopie-8.2.2/lib/ghc-8.2.2 many of these seems installed already.
Here's a (long) alternative answer. Note that I used to recommend Stack for beginners, too, but I've since changed my mind.
TL;DR: Either Haskell Platform or a pure Stack installation can provide you with everything you need, and you won't be "missing" anything by choosing one or the other. You'll probably find it easiest to skip Stack and install Haskell Platform using the "Generic" Linux installer, because it comes with everything you need and the setup will more closely matched what's described in the LYAH book. You can install Stack later when you're doing more serious development on multiple projects. If you prefer to stick with a pure Stack installation, I'd suggest starting with a "global project only" workflow. Either way, you can use "haskell-mode" with some configuration fixes suggested below (including a key setting that will be required if you're working in the global project of a Stack-only installation).
Here's the long answer...
Stack vs. Platform vs. Cabal
The LYAH book pre-dates Stack, which is certainly the main reason it doesn't mention it. At haskell.org, they recommend using either a minimal installer, Stack, or the Haskell Platform. All three methods are perfectly reasonable ways in 2018 to set up a working Haskell environment. They differ both in the ways they choose to isolate different versions of the compiler and/or libraries into "sandboxes" for development work, and in how much they install initially, but there's nothing "missing" from any one of them that can't be installed on demand. Depending on which you choose, there will be some differences in your workflow (see below).
Both Stack and Cabal are combined package managers and build tools. (Stack has the added ability to actually bootstrap an entire Haskell installation, which is why it's also an installation method in its own right.) While you're working through LYAH, you won't actually be using the "build tool" functionality directly on your own projects. (The built-in build facilities of GHC are more than adequate for building small, multi-module projects.) You'll just need the package manager functionality to install additional libraries.
Since Stack and Cabal manage their packages separately, if you're using Stack, you'll have no particular need to use Cabal directly. You can install it if you want (and in fact, Stack makes use of Cabal for some esoteric functionality, like "stack solver", and will require it to be installed in those cases):
$ stack install cabal-install
But, even though this will put "cabal" into "$HOME/.local/bin" (and you'll want to make sure this is in your path), you'll find that you need to jump through hoops to run it:
$ stack exec --no-ghc-package-path cabal -- list
and it doesn't really do anything useful as far as your Stack environment is concerned.
Update: A note on the "$HOME/.local/bin" path. It looks like the installation script from https://get.haskellstack.org/ may install Stack itself to /usr/local/bin/stack by default if there's no existing installation. However, it should display a warning to put $HOME/.local/bin in your path. If you upgrade Stack in the future with stack upgrade, it'll install the new version of stack there, and that directory will also be used if you install packages that include binaries. For example, stack install hlint will install the Haskell Lint program hlint to that directory. So, it's a good idea to have it in your path and somewhere before /usr/local/bin.
What's Missing with Stack
I think that covers your first three questions. For your last, the main thing you're missing having installed Stack instead of the Haskell Platform is that, by design, Stack doesn't really install anything globally other than "stack" itself. So, all your Haskell work including running the Haskell interpreter ("ghci") or compiler ("ghc"), all needs to be done within a Stack environment, either using a specific corresponding Stack command:
$ echo 'main = putStrLn "Hello, world!"' > Hello.hs
$ stack ghc -- Hello.hs
[1 of 1] Compiling Main ( Hello.hs, Hello.o )
Linking Hello ...
$ ./Hello
Hello, world!
$
or else using "stack exec" to run a generic program within an appropriate Stack environment. For example, it can sometimes be helpful to run a Bash shell under stack, after which things behave sort of like a globally installed Haskell Platform environment:
$ stack exec bash
$ ghci
GHCi, version 8.2.2: http://www.haskell.org/ghc/ :? for help
Prelude> :quit
$ ghc -O2 Hello.hs
[1 of 1] Compiling Main ( Hello.hs, Hello.o ) [flags changed]
Linking Hello ...
$ exit
$ ghc
The program 'ghc' is currently not installed. ...
$
The other thing you're missing is that the Haskell Platform installs a whole bunch of common libraries by default, while a fresh Stack environment starts with almost nothing (not even the compiler, before you run stack setup). While working through LYAH, you may find you need to periodically install additional libraries. For example, in the Input and Output chapter, the examples using random numbers (module System.Random) will require you to run:
$ stack install random
and restart your interpreter.
Recommendation to Use Haskell Platform
Because Stack is a little complicated and you won't really need the facilities it provides at the beginning, you may find the Haskell Platform easier to use when you're starting out. (The "Generic" installer should work fine on your distribution.) It comes with everything installed, and the way you use it will more closely match the way things are described in LYAH. Together with haskell-mode, you should have a pretty decent Haskell environment.
In general, there should be no issue having Stack and the Haskell Platform installed side-by-side (as evidenced by the fact that Haskell Platform actually includes Stack). Stack will maintain everything separately under the "$HOME/.stack" subdirectory, so there will be no interference between compilers or packages or anything. Note that in this setup, you'll use cabal to manage the packages installed on the Platform side of things, and stack -- obviously -- to manage packages on the Stack side.
Beginner Workflow for a Pure Stack Installation
If you want to stick with your pure Stack installation, I might suggest the following workflow when you're starting out:
You will see references to Stack projects, created with "stack new" or "stack init". Avoid these at the beginning, and stick with the stack "global project". This is the implicit project that will be in effect when you run "stack" in a directory that doesn't have a "stack.yaml" file (directly or in a parent directory):
$ cd
$ stack path --project-root
/u/buhr/.stack/global-project
$
When you're working in the global project (i.e., not somewhere under a stack.yaml file), you can invoke the interpreter and compiler with:
$ stack exec ghci
$ stack ghc -- -O2 Hello.hs
and they will both have access to any additional libraries (packages) you've installed using commands like:
$ stack install random
Updated: A note on the difference between stack ghci and stack exec ghci. The former is intended to run GHCi within the context of a local project (i.e., working under a stack.yaml file). It passes some additional flags to hide globally installed packages and to automatically make available modules from your package. When working in the global project, I don't think there's any practical difference except that stack ghci generates a warning; and no matter which you use, you'll need to load your own modules explicitly with :load Whatever.hs. There's a little more info on the difference on this Stack documentation page, particularly at the bottom where it tries to explain the difference.
Eventually, you may switch to a workflow that uses Stack projects. This will involve using stack new to create a new Stack project directory, stack setup to install/link a private compiler version into that directory, and then modifying the project's xxx.cabal file (and possibly its stack.yaml file) to indicate which additional packages are required, instead of using stack install. It's all a little complicated when you just want to get started writing code.
You may also see reference to Intero, an Emacs mode designed specifically for Stack. Intero is very nice, but it doesn't work very well when working on files in the global project. It'll tend to want to start up the interpreter in the directory "~/.stack/global-project", which is pretty useless. (I use Intero, but I've patched it to behave better in this respect.)
Configuring Haskell-Mode (for Either Platform or Stack)
It's probably best to stick with "haskell-mode" instead, and think about Intero when you start using non-global projects. I'd suggest installing "haskell-mode" from MELPA as per the instructions, but adding the following to your .emacs file instead of what's suggested in the documentation:
(require 'haskell)
;; add capability to submit code to interpreter and mark errors
(add-hook 'haskell-mode-hook 'interactive-haskell-mode)
;; add missing keybindings for navigating errors
(define-key interactive-haskell-mode-map (kbd "M-n") 'haskell-goto-next-error)
(define-key interactive-haskell-mode-map (kbd "M-p") 'haskell-goto-prev-error)
(define-key interactive-haskell-mode-map (kbd "C-c M-p")
'haskell-goto-first-error)
;; merge this with your existing custom-set-variables
(custom-set-variables
;; NOTE: include following line to work around haskell-mode
;; bug if using GHC >= 8.2.1.
;; See: https://github.com/haskell/haskell-mode/issues/1553
'(haskell-process-args-stack-ghci
'("--ghci-options=-ferror-spans -fshow-loaded-modules"
"--no-build" "--no-load"))
;; some options suggested in the haskell-mode documentation
'(haskell-process-auto-import-loaded-modules t)
'(haskell-process-log t)
'(haskell-process-suggest-remove-import-lines t)
;; make sure "stack ghci" is used, even in the global project
'(haskell-process-type 'stack-ghci))
I've tested this with a pure Stack installation using "haskell-mode-20171022.26", and it seems to work fine. I can load a new Haskell file in the global project, submit it to an interactive session with "C-c C-l", and browse highlighted errors in the source file with "M-n" and "M-p". (The errors appear in the mini-buffer.)
If you decide to use the Haskell Platform instead, I think all of this "haskell-mode" configuration will still apply, except you should remove the very last customization line. (The default haskell-process-type of auto will pick something appropriate.)
Hope that helps!
You have three choices.
Haskell Platform
It is a possibility but not a popular choice for many reasons which you will discover in due time if you choose to go this way. You will have a much better experience and get much better support with either Stack or Nix. Which of those two people use seems to be mostly about personal preference. They are different beasts but to a beginner the differences will not be immediately obvious so there's little hope that you will be able to make an "informed decision". Just pick one and reevaluate later.
Stack
This is what I would suggest to anyone (not familiar with Nix) wanting to get started with Haskell quickly. Period. You do not need to separately install anything, Stack will handle all the Haskell stuff for you. You don't normally ever use cabal directly with Stack. stack build uses cabal internally but you don't need to worry about that. One thing to note, Stack is not a package manager. It's a build tool. It doesn't normally install anything. It does however fetch all the dependencies that it needs and stores them in ~/.stack together with other things.
Nix
This is what I use personally so I may be biased but I think this is the best solution overall in the long term. The caveat is that there is a rather steep learning curve and you are given many chances to shoot yourself in the foot when starting out.
I highly recommend starting with Stack but keeping an open mind about Nix as your journey with Haskell continues.
I am little confused about why this doesn't work.
I have a small program that import System.Directory. When I run it with runhaskell on the command line it compiles and outputs what I expect.
When I use the same program with stack I get a message saying
Failed to load interface for ‘System.Directory’
It is a member of the hidden package ‘directory-1.3.0.0’.
Use -v to see a list of the files searched for.
I dont understand why it would work with runhaskell but not when i use stack ghci
With the information you give, I can only attempt a guess…
I think you have directory (globally) installed with cabal install directory or as a system package - this would explain runhaskell myscript.hs working.
if you use stack you have the following options.
make a cabal package, add directory to the build depends section, create a stack.yaml and run stack ghci inside the project directory.
use stack ghci --package=directory myscript.hs
I've done stuff in agda as a hobby for a few months now, and I started to make a provably safe\correct Tic Tac Toe game.
I've got all the lemmas proofs and definitions, but now that I have tried to get input and print output I've ran into a problem.
All "Hello World" examples taken from the web have failed, most of them with the message that I am missing Data.FFI and IO.FFI.
I've looked around for a solution online,, but none were of use. One website said I should run "cabal install" from agda/agda-stdlib-0.11/ffi but I"m not even sure if I have that folder on my computer, and I have many folders named "agda", all over the computer (this is my first time using linux for something, so I probably did stuff horribly)
This is the error I get when trying to run the code from EMACS with agda-mode (C-c C-x C-c)
Compilation error:
MAlonzo/Code/Agda/Primitive.hs:4:18:
Could not find module ‘Data.FFI’
Use -v to see a list of the files searched for.
MAlonzo/Code/Agda/Primitive.hs:5:18:
Could not find module ‘IO.FFI’
Use -v to see a list of the files searched for.
If it matters, I'm running Ubuntu.
Thank you very much for the help!
One website said I should run "cabal install" from agda/agda-stdlib-0.11/ffi
That is correct. From the README for the standard library 0.11:
-- To compile the library using the MAlonzo compiler you first need to
-- install some supporting Haskell code, for instance as follows:
--
-- cd ffi
-- cabal install