Previously I used ghc version < 8 on Linux and when I had a script in a file, say file.hs, like
let x = "hello"
putStrLn x
double x=2*x
print $ double 2
double 3
then it was possible to run it and get the outputs in a terminal by doing
ghc -e ':script file.hs'
Now I'm using ghc 8.0.1 on Windows and this does not work anymore. Is there another way ?
I can get the outputs if I open GHCi and type :script file.hs. But I want these outputs in the terminal.
I don't know whether this is due to the upgrade of ghc or to the OS.
This works with double quotes:
ghc -e ":script file.hs"
Related
I'm trying to run a .ml script, test.ml, using the command ocaml and use a module, template.ml, that I setup.
Currently, I know that I can run ocaml using the module by doing ocaml -init template.ml and that I can run a script using ocaml test.ml.
I'm trying to run the script, test.ml, and use the module, template.ml.
I have tried using ocaml test.ml with the first line being open Template ;;after compiling template with ocamlopt -c template.ml. Template is undefined in that case.
I have also tried using ocaml -init template.ml test.ml with and without open Template ;; as the first line of code. They don't work or error respectively.
First, the open command is only for controlling the namespace. I.e., it controls the set of visible names. It doesn't have the effect (as is often assumed) of locating and making a module accessible. (In general you should avoid over-using open. It's never necessary; you can always use the full Module.name syntax.)
The ocaml command line takes any number of compiled ocaml modules followed by one ocaml (.ml) file.
So you can do what you want by compiling the template.ml file before you start:
$ ocamlc -c template.ml
$ ocaml template.cmo test.ml
Here is a fully worked example with minimal contents of the files:
$ cat template.ml
let f x = x + 5
$ cat test.ml
let main () = Printf.printf "%d\n" (Template.f 14)
let () = main ()
$ ocamlc -c template.ml
$ ocaml template.cmo test.ml
19
For what it's worth I think of OCaml as a compiled language rather than a scripting language. So I usually compile all the files and then run them. Using the same files as above, it looks like this:
$ ocamlc -o test template.ml test.ml
$ ./test
19
I only use the ocaml command when I want a to interact with an interpreter (which OCaml folks have traditionally called the "toplevel").
$ ocaml
OCaml version 4.10.0
# let f x = x + 5;;
val f : int -> int = <fun>
# f 14;;
- : int = 19
#
How can I replicate ghci -e "print 123" in cabal v2-repl?
I've searched for "expression" or "statement" in cabal v2-repl --help with no luck.
The simplest way is to use shell piping capabilities. See:
% cabal v2-repl <<< ':type zip'
...
λ zip :: [a] -> [b] -> [(a, b)]
λ Leaving GHCi.
This <<< notation, in sh script interpreter, means that the quoted string is sent to the standard input of the command, followed by newline, then end of file.
There are other ways. For example, if you wish to supply more lines, you can use the so-called "here-doc":
% cabal repl <<EOF
:type zip
:type fst
EOF
The <<< notation is a shorthand for a one-line "here-doc".
In general, a program may know whether its standard input is a terminal (assuming, live user) or a file (which heredoc pretends to be), and behave differently. But ordinarily it would work either way, and, if you can send things to its standard input, you can automate it.
I'm fairly new to NixOS, and am trying to invoke emacs from a Haskell program using the following function:
ediff :: String -> String -> String -> IO ()
ediff testName a b = do
a' <- writeSystemTempFile (testName ++ ".expected") a
b' <- writeSystemTempFile (testName ++ ".received") b
let quote s = "\"" ++ s ++ "\""
callCommand $ "emacs --eval \'(ediff-files " ++ quote a' ++ quote b' ++ ")\'"
When I run the program that invokes this command using stack test, I get the following result (interspersed with unit test results):
/bin/sh: emacs: command not found
Exception: callCommand: emacs --eval '(ediff-files "/run/user/1000/ast1780695788709393584.expected" "/run/user/1000/ast4917054031918502651.received")'
When I run the command that failed to run above from my shell, it works flawlessly. How can I run processes from Haskell in NixOS, as though I had invoked them directly, so that they can access the same commands and configurations as my user?
Both your shell and callCommand use the PATH environment variable, so it seems like stack is changing that. It turns out that stack uses a pure nix shell by default, but you also want to access your user environment, which is 'impure'.
To quote the stack documenation
By default, stack will run the build in a pure Nix build environment (or shell), which means the build should fail if you haven't specified all the dependencies in the packages: section of the stack.yaml file, even if these dependencies are installed elsewhere on your system. This behaviour enforces a complete description of the build environment to facilitate reproducibility. To override this behaviour, add pure: false to your stack.yaml or pass the --no-nix-pure option to the command line.
Another solution is to add Emacs to nix.dependencies in stack.yaml (thanks #chepner). It has the benefit that some version of Emacs will always be available when a developer runs the tests, but that Emacs may not be the Emacs they want to use. You may be able to work around that using something like ~/.config/nixpkgs/config.nix, unless they have configured their Emacs elsewhere, like the system configuration or perhaps a home manager. I'd prefer the simple but impure $PATH solution.
I've installed the Haskell platform on my mac (OSX lion), and ghci is running great.
Now I've created a haskell-file, stored on my "desk." How can I call it from this directory?
Example:
Prelude> :load datei.hs
[1 of 1] Compiling Main ( datei.hs, interpreted )
datei.hs:1:7: parse error on input `\'
Failed, modules loaded: none.
datei.hs:
let fac n = if n == 0 then 1 else n * fac (n-1)
Why do I get this?
Use the OSX terminal to reach your desktop and invoke yourfile.hs using ghci:
cd ~/Desktop
ghci yourfile.hs
edit:
As stated in the comments, the error message you're seeing above is warning you that the character \ exists at an unexpected location in the source code.
Since that character does not exist in the line of code you posted, there must be more to datei.hs. We need to see the rest of your source code before we can help.
If you saved your program with TextEdit, it's very possible that you're seeing a '\' character because you're saving it as an RTF file (TextEdit's default). Hit Ctrl-shift-t to convert it into a plain text file.
If your already in ghci you can use ':cd /path/to/file' as well.
Here is a good thread discussing let.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Outputting Haskell GHCi command results to a txt file
I am new to Haskell and I am trying to redirect test cases output results to a text file. The way it is set up now, is a AddAllTestCases.hs contains all the test cases I need to run in order to test a function I created. I run the test cases on GHCi by loading AddAllTestCases.hs and then simply typing main and hitting enter. That causes test case output results to print inside the GHCi perfectly.
Because there hundreds of test cases, I need to redirect output results to text file.
Attempt #1:
writeFile "myoutput.txt" $ show $ main
I get the following error:
No instance for (Show(IO())) arising from a use of show
Attempt #2 in CMD (trying to create an executable, then outputting executable results to text file):
ghc --make AddAllTests.hs -o testResults.exe
Which gives me the following error:
Warning: output was redirected with -o, but no output will be generated because there is no Min module
This is weird because when I am using GHCi (attempt #1) and I type in main it executes everything perfectly, which I would assume, implies that there is a main module?
I greatly appreciate any help with redirecting test case results to a text file.
Many thanks in advance!
You need a Main module (and a main action) to produce an executable. You can rename your module to Main, or you can specify the module to be considered Main on the command line,
ghc --make -main-is AddAllTests AddAllTests.hs -o testResults.exe
to produce an executable without a module named Main.
A method without compiling would be
ghc AddAllTests.hs -e "main" > testResults.txt
Another method would be to have a file in which you just list all test cases,
3 + 2 :: Rational
reverse "foobar"
:q
and run ghci with redirected in- and output
ghci < testCases > testResults.txt