I've read in the utf8-string package that ghc should support utf8 by default. I've even seen somewhere being written that now my default codepage is used.
Despite all that, a simple code does not execute.
writeFile "asd.txt" "ćlččć"
returns
*** Exception: filenames.txt: commitBuffer: invalid argument (invalid character)
How do I get this code to execute?
Perhaps you should set the encoding of the handle you're actually writing to. I don't know for sure, since I can't reproduce your problem, but something like this may do:
withFile "asd.txt" WriteMode $ \h -> do
hSetEncoding h utf8
hPutStr h "ćlččć"
Related
Vim has the possibility to let you replace selected text with the output of an external program. I'd like to take advantage of this with programs that I'd write in Haskell. But it doesn’t get the selected text as args.
-- show-input.hs
module Main where
import System.Environment
main = do
input <- getArgs
putStr ("Input was: " ++ (show input))
When I run it from the command line (NixOS GNU/Linux, BASH), I get the expected behavior:
$ ./show-input test
Input was: ["test"]
When I select some text in Vim and invoke :'<,'>!~/show-input, I get this :
Input was: []
There is something weird here, but I can't tell if it is from the way Vim passes arguments or from the way Haskell gets them. I have tried with both console Vim and graphical gVim (8.0.1451), with the same result.
NB: I can successfully use Vim Bang! with other external programs, such as grep. It works great.
---
Correct version after chepner's answer
So, for anyone interested, just replace getArgs with getContents and you get your input all in a string (instead of a list of strings).
module Main where
import System.Environment
main = do
input <- getContents
putStr ("Input was: " ++ (show input))
The ! command sends the seleted text to the program via standard input, not as a command line argument. The command line equivalent would be somecommand | ./show-input.
I apologize if this is a simple question.
I have specified an input file which is in the same directory of the code source file.
isprime :: Int -> [Int] -> Bool
isprime ...
main = do
handle <- openFile "primes-to-100k.txt" ReadMode
contents <- hGetContents handle
i <- getLine
print $ isprime (read i::Int) $ map (\x->read x::Int) $ lines contents
hClose handle
The code runs well when I use "runhaskell Q111.hs" in shell,
but when I compile it with "ghc --make Q111.hs and run, I got an error message
Q111: primes-to-100k.txt: openFile: does not exist (No such file or directory)
logout
The point is that the code runs well with ghci and runhaskell, but the executable can't find the input txt.
Do I have to provide the input txt to compiler using someway?
How are you running the executable? The text file would have to be in the directory you run the program from, which may or may not be where the program is. If you are running ./Q111 from the command line, or if you are double-clicking Q111.exe in Windows, then the text file must be in the same folder as the executable. If you are in a different directory on the command line, then the text file would have to be wherever your current directory is, and not the directory where the executable is.
EDIT: Just saw from your other comment that you are on OS X, and (I assume) are double-clicking the program. From what you said I guess that OS X sets the current directory of such-executed programs to be your home. If you want to get the directory of your program, see the answers to this question. If you use the FindBin package they mention:
main = do
exedir <- getProgPath
handle <- openFile (exedir ++ "/primes-to-100k.txt") ReadMode
...
Try the curdDir <- getCurrentDirectory and paths <- getDirectoryContents and check the paths. If it contains the filename, the path is right(and try using contents <-readFile "file" for simpler programs, but this isn't neccessary).
Edit:
...and use isexist <- doesFileExist "f" for checking the existence.
I have a bit of code in my haskell program like so:
evaluate :: String -> IO ()
evaluate = ...
repl = forever $ do
putStr "> " >> hFlush stdout
getLine >>= evaluate
Problem is, when I press the delete key (backspace on windows), instead of deleting a character from the buffer, I get a ^? character instead. What's the canonical way of getting delete to delete a character when reading from stdin? Similarly, I'd like to be able to get the arrow keys to move a cursor around, etc.
Compile the program and then run the compiled executable. This will give the correct behavior for the Delete key. For some reason interpreting the program screws up the use of Delete.
To compile the program, just invoke ghc like this:
$ ghc -O2 myProgram.hs
This will generate a myProgram executable that you can run from the command line:
$ ./myProgram
That will then give the correct behavior for Delete.
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.
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.