I compiled my helloworld.hs and got a helloworld.o file, I tried ./helloworld, but it didn't work, so what is the right way to execute the helloworld?
I am using cygwin, I just write down $ ghc --make helloworld.hs and I get helloworld.hi, helloworld.exe.manifest, helloworld.o files, I don't know what do I need to do next...
Depending on whether you used a Cygwin ghc or a Windows native ghc, you got either a.out (a historical traditional name) or helloworld.exe. If you have a.out you'll need to rename it to something.exe to execute it on Windows.
You can easily tell ghc how to call the executable: ghc -o helloworld.exe --make helloworld.hs.
By the way ghc --help would have told you:
To compile and link a complete Haskell program, run the compiler like so:
ghc-6.8.2 --make Main
where the module Main is in a file named Main.hs (or Main.lhs) in the current directory. The other modules in the program will be located and compiled automatically, and the linked program will be placed in the file a.out' (orMain.exe' on Windows).
As you haven't specified anything about how you compiled, such as for instance what compiler you're using, we can only guess.
The common way to get a .o (object) file out of ghc is using the -c switch; as the manual says, that means "do not link". The mnemonic is "compile only". Without linking, you have only a portion of a program, and it cannot be executed. Precisely what it needs to be linked against will depend on the particular object file, and some of that is filled in by default if you simply let the compiler run the linker. Linking separately is more complicated.
Related
This is a follow-up to this question, which is about whether it is possible to compile simple programs on Haskell in Windows, without recourse to Cygwin: Compiling Haskell programs in Windows: is it possible without downloading something such as Cygwin?
For background, I asked this question, 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)
Someone responded to my question, suggesting I open the command line and put ghc --make helloworld and hit Enter. However, when I put in ghc --make helloworld and hit Enter this comes up:
ghc: unrecognised flag: --
did you mean one of:
-D
-F
-H
Usage: For basic infomration, try the '--help' option
The person answering the question suggested I made another question, asking why I received the above message. How can I deal with this problem?
Yes, it is possible to use Windows to compile Haskell programs. In fact, I use Windows for all my Haskell programming! To compile a Haskell program, use ghc --make <program>; for instance, here it would be ghc --make helloworld.hs. Note that there is no space between -- and make; including this space gives the error you describe. After running this command, an executable helloworld.exe file is produced.
I'm compiling my myProgram.lhs with the use of a cabal sandbox (set up with cabal sandbox init). I'm using a simplest approach I've come up with:
cabal exec -- ghc myProgram
or (having a rule in Makefile)
cabal exec -- make myProgram
After that, in my source directory, appears myProgram.o, but not the executable myProgram.
How do I run the resulting program?
cabal exec -- ./myProgram
doesn't work.
Now, I've come up with a simplest approach to test it:
cabal exec -- runghc myProgram.lhs
but I don't like this.
Do you know where the resulting executable is?
(I haven't created any cabal file for my project yet. I simply used to compile the program with bare ghc and test it, then--when I needed custom dependencies--I set up the cabal sanbox and installed the dependencies manually there.)
This didn't actually look like a problem of cabal exec, and it wasn't!
My history
Simultaneously with starting to use the cabal sandbox, I explicitly gave a custom name to my module in the source file (myProgram.lhs). And in such case just a bare ghc (without cabal exec) wouldn't generate the executable, too, as answered in Cabal output is redirected but not generated. (I simply couldn't test the bare ghc command, because I had the dependencies in the sandbox, so my module wouldn't compile.)
Explanation
Explanation quoted from that Q&A:
I get the warning
output was redirected with -o, but no output will be generated because there is no main module.
A quote from The Haskell 98 Report:
A Haskell program is a collection of modules, one of which, by convention, must be called Main and must export the value main.
The solution
A solution is to add -main-is MyProgram.main to ghc opts. Then it generates the executable.
./myProgram simply appears in my source directory now, no matter whether I call
ghc -main-is MyProgram.main myProgram
or
cabal exec -- ghc -main-is MyProgram.main myProgram
I have a Haskell project where a number of executables are produced from mostly the same modules. I'm using a Makefile to enable parallel builds, and it very nearly works the way I want. Here's a stripped down version of my current Makefile, with ideas taken from http://www.haskell.org/ghc/docs/latest/html/users_guide/separate-compilation.html#using-make:
HFLAGS=-O3 -Wall -v0 -fno-ignore-asserts
HASKELLS=bin1 bin2 bin3 bin4 bin5 bin6 bin7 bin8 bin9
all: $(HASKELLS)
%.hi: %.o
#:
%.hi %.o: %.hs
ghc -c $(HFLAGS) $<
$(HASKELLS): %: %.o
ghc --make $(HFLAGS) $#
.hsdepend: *.hs
ghc -M -dep-makefile .hsdepend *.hs
rm -f .hsdepend.bak
include .hsdepend
As you can see, I still use ghc --make for linking (only); this way the individual modules can be compiled in parallel, and ghc --make only invokes the linker.
Unfortunately this is not foolproof: A relink is triggered only for, say, bin1 only if bin1.o is newer than the executable, but not if only one of the other object files has been updated. This can happen when a change is made in a module such that it results in the .o file being updated, but the interface of the module does not change, i.e. the .hi file is not touched.
One alterative solution would be to trigger a null ghc --make for every binary every time make is invoked; unfortunately, this is slow and clutters the output (I'd like to see when something was linked and when not).
ghc -M only generates a dependency line for each .o file, but none for the linked executables. The information about which .o files to link into which executable (given the name of the main module binN.hs) obviously is there, but it's not entirely clear to me if it's possible to get to it using any Makefile magic.
I can only think of a way to do what this by writing a post-processor for .hsdepend, but that seems excessive.
Can anyone suggest a better solution?
My advice would be, don't bother trying to make this work. It should work, and it would be nice if it worked, but ghc's -M support is currently broken (as in, it doesn't generate proper dependency rules, and omits rules for some non-Haskell files). Actually getting this to work reliably will take a great deal of effort, and in the end will trigger more rebuilds than strictly necessary.
Furthermore, support for parallel builds has been merged into GHC, so when ghc-7.8 is released you'll be able to use plain ghc --make to get parallel builds. Or you could use ghc's HEAD now.
I've got a Haskell file, Saturn.hs, and a C++ file hssaturn.cpp and hssaturn.h, in the directory src/Galakhsy/. hssaturn.cpp needs libsaturn.cpp and/or libsaturn.hpp, which are in lib/saturn/src/lib/.
I have no idea how to compile it properly, any pointers?
Compile all the C++ files to object files using g++ -c filename.cpp. This produces, in your case, hssaturn.o and libsaturn.o. Then compile your Haskell program with ghc --make -o whatever Saturn.hs hssaturn.o libsaturn.o. Also specify any shared libraries needed by the C++ stuff with -lblabla. You probably at least need the C++ standard library, i.e. -lstdc++, making the GHC command something like
ghc --make -o whatever Saturn.hs hssaturn.o libsaturn.o -lstdc++
(well, modulo the correct paths for the two object files).
Also remember to prevent name mangling by using extern "C" for the C++ functions you call from Haskell.
Addendum: The name libsaturn makes me think it is perhaps a library. You might want to consider compiling it as that and simply linking dynamically (with the -l switch to GHC as above).
I have a program, say src/sample.hs, and I want it to compile (using ghc --make) to build/sample.exe.
I've figured out how to map the .hi and .o files over to the build folder, but I can't seem to find anything on how to compile the executable to a different directory. Does anyone know how to do this?
Thanks!
How about explicitly setting the output filename including the directory? Works over here, I haven't tested on Windows so I'm not sure if you need the .exe extension or not.
ghc --make -o build/sample.exe src/sample.hs
Also worth noting: --make is enabled by default as of GHC 7.0.