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.
Related
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"
Is it possible to get the absolute path of the current source file in Haskell?
I could only find one relevant function: getCurrentDirectory from System.Directory, but it "returns an absolute path to the current directory of the calling process.", not the path of the current file.
(I need it to read sample inputs which are located in the same folder as the source file; If there's any better way to do it, that will be helpful too!)
You can use CPP. If you compile this file
{-# LANGUAGE CPP #-}
main = print __FILE__
it will print the path to the source as you passed it to ghc – which may or may not be the full path, though:
/tmp $ ghc --make mypath.hs
[1 of 1] Compiling Main ( mypath.hs, mypath.o )
Linking mypath ...
/tmp $ ./mypath
"mypath.hs"
/tmp $ ghc --make /tmp/mypath.hs
Linking /tmp/mypath ...
/tmp $ ./mypath
"/tmp/mypath.hs"
As an alternative, the file-embed package can be used here. It uses template haskell to embed files/directories.
This can be very useful to embed resources or configs in the executable. It may not be advisable to read the sample input this way though. data-files in cabal might be better alternative as already pointed out earlier in this thread.
The PseudoMacros package might be useful. According to the description, it provides C-like strings for the current file name etc.
UPDATE
The file name returned by PseudoMacros equals the path passed to ghc (same behaviour as #JoachimBreitner mentioned in his answer), so
import PseudoMacros
main :: IO ()
main = putStrLn ("Hello from " ++ $__FILE__ ++ ", line " ++ show $__LINE__ ++ "!")
will print
Hello from tmp.hs, line 5!
or
Hello from /tmp/tmp.hs, line 5!
depending on whether you provided a relative or absolute filename to ghc.
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
I have developed a haskell application which is tested with WinHugs interpreter working fine .. when i try to comiple the same application using WinGHCi it prompts a error
lexical error in string/character literal at character '\t'
I have used \t in IO Program to display text
Example :- putStr "\n \n \t \t Hello ! "
Any solutions ?
You may want to try this step-by-step guide:
Save your program in a file program.hs this file should contain a function main of the type IO () that is executed at the program's start.
Open a shell in the directory where this file is.
Type ghc -O3 --make program.hs to compile program.hs into an executable program.exe.
Try to run program.exe
If the error still occurs, please post some more code to aid debugging.
I just want to read (and maybe write) UTF-8 data. haskell.org still advertises System.Streams which does not compile with recent ghc:
% runhaskell Setup.lhs configure
Configuring Streams-0.2.1...
runhaskell Setup.lhs build
Preprocessing library Streams-0.2.1...
Building Streams-0.2.1...
[10 of 45] Compiling System.FD ( System/FD.hs, dist/build/System/FD.o )
System/FD.hs:138:22:
Couldn't match expected type `GHC.IOBase.FD'
against inferred type `FD'
In the first argument of `fdType', namely `fd'
In a 'do' expression: fd_type <- fdType fd
In the expression:
let
oflags1 = case mode of
ReadMode -> ...
WriteMode -> ...
ReadWriteMode -> ...
AppendMode -> ...
binary_flags | binary = o_BINARY
| otherwise = 0
oflags = oflags1 .|. binary_flags
in
do fd <- fdOpen filepath oflags 438
fd_type <- fdType fd
when (mode == WriteMode && fd_type == RegularFile)
$ do fdSetFileSize fd 0
....
Similar problem with Streams 0.1. I cannot get more recent versions since the official site is down:
% wget http://files.pupeno.com/software/streams/Streams-0.1.7.tar.bz2
--2009-07-30 15:36:14-- http://files.pupeno.com/software/streams/Streams-0.1.7.tar.bz2
Resolving files.pupeno.com... failed: Name or service not known.
wget: unable to resolve host address `files.pupeno.com'
A better solution? darcs source code?
Use the utf8-string or the more recent text package.
View the list of packages on hackage.
Edit:
L. Kolmodin is right: utf8-string or text is the right answer. I'll leave my original answer below for reference. Google seems to have steered me wrong in choosing IConv. (The equivalent of my IConv wrapper function is already in utf8-string as Codec.Binary.UTF8.String.encodeString.)
Here is what I've been using--I may not remember the complete solution, so let me know if you still run into problems:
From Hackage, install IConv. Unfortunately, Codec.Text.IConv.convert operates on bytestrings, not strings. I guess you could read files directly as bytestrings, but I wrote a converter since HaXml uses normal strings:
import qualified Data.ByteString.Lazy.Char8 as B
utf8FromLatin1 = B.unpack . convert "LATIN1" "UTF-8" . B.pack
Now, on Mac OS, you have to compile with
$ ghc -O2 --make -L/usr/lib -L/opt/local/lib Whatever.hs
Because there was some library conflict, I think with MacPorts, I have to point explicitly to the built-in iconv libraries. There is probably a way to always pass those -L flags to ghc, but I haven't looked it up yet.
utf-8 strings are just byte character sequences, so it should be possible to just read and write the strings as is. All of the first 127 characters, including whitespace, should be ascii. Of course, you would need your own functions for manipulating strings since they are now multi byte sequences.