I have installed Haskell platform following the instructions on chocolatey and haskell.org.
I am using Windows 10.
My hello.hs program complies in command prompt, but when I try to do the same in VS code,
it won't load Prelude, which I assume is necessary for running Haskell programs.
I think it might be a configuration problem, but I cant find any useful documentation on it.
How could I fix this and turn on Prelude?
Are the problems that VS code shows relevant to this problem?
Nothing looks wrong in your screenshots. The prompt text is ghci> rather than Prelude> because GHCi no longer defaults to showing the loaded modules on the prompt (see the GHC 9.0.1 changelog. Prelude is being loaded regardless. The warning shown in the IDE is a style suggestion that is inconsequential for the purpose of getting your code to run. As chi suggests, :l hello.hs at the GHCi prompt should be enough to have it loaded.
If I type main into the console, then it works
ghci> main
"haskell"
name
"hi, name"
ghci>
This might work
$ ghci
ghci> import Prelude
Prelude> printStrLn "Hello World!"
Hello World!
Prelude>
You may need to just run import Prelude.
Related
I'm using stack ghci to start my REPL, based on the answer I got for my question on how to import a module installed with stack. This works fine, but I get initially a warning message Note: No local targets specified, so a plain ghci will be started with no package hiding or package options., followed by a bunch of suggestions about package hiding and options. My guess is that this is because I have not used stack init to setup a project, since I am still in the "playing around and learning" state and don't want a project yet. I have not found an explanation about the meaning of 'no local targets', but the effect to start a plain ghci is exactly what I want at that point. Is there a way to suppress this message? I looked at stack --help, but could not find something suitable.
As the Note (not warning) suggests, a plain ghci is started, which is rather uncommon situation when working with stack.
~$ stack ghci
Note: No local targets specified, so a plain ghci will be started with no package hiding or package options.
You are using snapshot: lts-14.12
If you want to use package hiding and options, then you can try one of the following:
* If you want to start a different project configuration than /home/username/.stack/global-project/stack.yaml, then you can use stack init to create a new stack.yaml for the packages in the
current directory.
* If you want to use the project configuration at /home/username/.stack/global-project/stack.yaml, then you can add to its 'packages' field.
Configuring GHCi with the following packages:
GHCi, version 8.6.5: http://www.haskell.org/ghc/ :? for help
Loaded GHCi configuration from /tmp/haskell-stack-ghci/2a3bbd58/ghci-script
Prelude>
This means though that all you need to do to get the same behavior without the Note is just start ghci manually in the context of global stack environment:
~$ stack exec -- ghci
GHCi, version 8.6.5: http://www.haskell.org/ghc/ :? for help
Prelude>
In case that you want to make sure some package is installed for "playing around and learning" in the ghci session you can supply them as --package arguments
~$ stack exec --package massiv -- ghci
atomic-primops> using precompiled package
cabal-doctest > using precompiled package
scheduler > using precompiled package
massiv > using precompiled package
Completed 4 action(s).
GHCi, version 8.6.5: http://www.haskell.org/ghc/ :? for help
Prelude> import Data.Massiv.Array
Prelude Data.Massiv.Array>
stack exec --ghci as in lehins's answer did not work for me, but stack exec ghci did.
I am using trace for debugging on Windows 10, and the terminal states that Logs printed to console, but I have no idea where to find this output.
As far as I can tell, console in Windows means the standard output stream. You can easily see trance output if you're running GHCi in the Windows Command Prompt, as this session demonstrates:
C:\Users\mark>stack ghci
Configuring GHCi with the following packages:
GHCi, version 8.0.2: http://www.haskell.org/ghc/ :? for help
Loaded GHCi configuration from C:\Users\mark\AppData\Local\Temp\ghci7560\ghci-script
Prelude> :m +Debug.Trace
Prelude Debug.Trace> foo x = trace "foo" x
Prelude Debug.Trace> foo 42
foo
42
Here, I'm using Stack to run Haskell, but IIRC, you can use the Haskell Platform for Windows in the same way.
I'm running:
GNU Emacs 24.4.1
Stack Version 1.3.3
org-mode
haskell-mode
I've looked through:
Emacs Org-Mode & Literate Haskell
https://gist.github.com/reetinder/4022989
https://wiki.haskell.org/Emacs/Literate_programming
https://wiki.haskell.org/Literate_programming
https://github.com/haskell/haskell-mode/issues/1429
While the gist above looks promising, I haven't found anything that looked to be an authoritative way to get org-haskell running (eg, nothing on melpa), and certainly nothing aimed specifically at whatever intricacy running a stack environment rather than using my global ghc would entail.
When I try to:
#+BEGIN_SRC haskell
let x = "test"
putStrLn x
#+END_SRC
I get
executing Haskell code-block
...which hangs forever. When I C-g, I see:
GHCi, version 7.6.3: http://www.haskell.org/ghc/ :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Some flags have not been recognized: prompt2, ghci |
ghci λ> let x = "TESTING!"
putStrLn x
"org-babel-haskell-eoe"
Prelude|
<interactive>:4:1: parse error on input `putStrLn'
ghci λ> "org-babel-haskell-eoe"
When I tab to the haskell buffer, I see it has genuinely evaluated what I sent, it just has this org-babel-haskell-eoe error and never returns control to my org session.
Any chance this is because I have a custom prompt? Using the lambda instead of Prelude> ?
This is not a complete answer: in particular, it does not even mention Stack. But I (a complete ignoramus on Haskell) wanted to find out what it would take to get the OP's test program to run in babel. Here's what I found:
You need a haskell interpreter ;-) I'm on Fedora 24, so I installed the ghc-compiler package and I got ghci.
You need haskell-mode. I installed that from MELPA, using the emacs package manager. That also installed inf-haskell.el
By default, inf-haskell wants to run hugs, so I customized haskell-program-name and set it to "ghci".
M-x load-library RET ob-haskell RET
C-c C-c on the code block: the first time it fails and the Messages buffer shows "Buffer haskell.org does not exist or has no process".
But if you do it C-c C-c on the code block again, it succeeds!
Obviously, ob-haskell.el needs some work - and that's before we even get to Stack, of which I know even less than I know of Haskell, so I'll leave that as an exercise for the interested reader :-)
EDIT: Re. version info (requested in a comment): I keep close to the bleeding edge. At this point in time (2017-05-01), I run Org mode version 9.0.5 (release_9.0.5-444-g998576 # /home/nick/elisp/org-mode/lisp/) and GNU Emacs 26.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.20.10) of 2017-04-14
It is probably because of the custom prompt: I had the same issue, and when I removed ":set +t" and ":set prompt "GHCI >" from ~/.ghci, it worked. I fiddled with it some, and it seems it will work so long as your custom prompt doesn't have any spaces in it except the end (I changes mine to "GHCI> " and it works). It seems to be that the regular expression it parses the information from assumes the prompt will have no spaces in it.
In my case it was .ghci, like Testare's. As soon as I commented out :set prompt "λ ", emacs stopped freezing but gave the message ‘org-babel-script-escape’ expects a string. It was necessary to comment out :set +t for it to work.
what i did after installed stack and ghci (with stack itself)), was to install intero in emacs and then add those to init.el:
(setq haskell-process-type 'stack-ghci)
((org-babel-do-load-languages
'org-babel-load-languages
'((haskell . t)))
after that i can C-c C-c in haskell code block and i get a result under the code block.
I can't figure out how to get WinGHCi to load and compile my .hs file.
I have a file, C:\Users\Haskell\Source\hello.hs, that only contains the following line:
main = putStrLn "Hello, world!"
If, at the Prelude> prompt, I run
:cd C:\Users\Haskell\Source\
nothing happens, which I'm assuming means the command was successful. However, when I try to run
:load hello.hs
I get a "[1 of 1] Compiling Main. Ok, modules loaded: Main" message. My prompt then changes from "Prelude" to "*Main" and I type:
ghc -o hello hello.hs
After that, I will get a series of errors talking about how ghc, o, hello, hello, and hs are "Not in scope."
I am in the correct directory. Why won't my program run?
One of my problems is that I'm unable to navigate the directories. I know that :!dir lists the files, and I am in the right directory, but :load hello.hs still doesn't work and I keep getting the scope error.
Any help would be appreciated.
EDIT: A user pointed out that if I have gotten to the *Main prompt, then my program has been loaded and compiled and I do not need to run the ghc command. If that is the case, how would I run it? Haskell.org states that, "You can then run the executable (./hello on Unix systems, hello.exe on Windows)," but an exe has not been created.
I find it easier to first navigate to the directory then invoke ghci. Once in Prelude you can use :l and the file name.
Or, you could load ghci then use :l and use the fully qualified path for the file.
Edit:
After reading your edits, it is clear you are getting your code compiled fine. Once it says it has compiled, there is no reason to try and do so again with ghc (I don't think you can do that from within ghci anyhow).
Now that it is compiled, you can use any of the code and data types defined there in. So to use your main function, just type in main at the *Main> prompt.
I'm trying to run some Safe Haskell code with runghc, but it doesn't seem to work for me.
bgeron#tinker:/tmp/wtf$ ls
Strange.hs
bgeron#tinker:/tmp/wtf$ cat Strange.hs
module Strange where
main :: IO ()
main = do
return ()
bgeron#tinker:/tmp/wtf$ runghc -XSafe Strange
Strange:1:1: Not in scope: `System.Environment.withArgs'
bgeron#tinker:/tmp/wtf$ runghc --version
runghc 7.6.3
I thought this would be a valid use of runghc; the error is most confusing. Is this a bug?
I'm using Ubuntu 14.04, 64-bit.
The observed behaviour can be explained by the following.
The implementation of runghc is here:
https://ghc.haskell.org/trac/ghc/browser/ghc/utils/runghc/runghc.hs
It will make the following call to ghc, which also shows the strange behaviour:
ghc -XSafe -e ':main' Strange.hs
The implementation of ghc in evalatue-expression mode will add the offending import:
https://ghc.haskell.org/trac/ghc/browser/ghc/ghc/InteractiveUI.hs#L1154
I am not sure whether it's a bug. I agree it's confusing.
As mentioned in the comment, just add import System.Environment