[[project @ 2002-04-30 16:34:12 by simonmar]
simonmar**20020430163412
Add a FAQ section. This will replace the mini-FAQ on the download
page (which we never really kept up to date), and will hopefully
accumulate all sorts of useful Q/As over time. Please feel free to
add to it...
] {
addfile ./ghc/docs/users_guide/faq.sgml
hunk ./ghc/docs/users_guide/faq.sgml 1
+
+ GHC FAQ
+
+ This section has the answers to questions that get asked
+ regularly on the GHC mailing lists, in no particular order. Please
+ let us know if you think there's a question/answer that should be
+ added here.
+
+
+
+ How do I port GHC to platform X?
+
+ There are two distinct possibilities: either
+
+
+ The hardware architecture for your system is already
+ supported by GHC, but you're running an OS that isn't
+ supported (or perhaps has been supported in the past, but
+ currently isn't). This is the easiest type of porting
+ job, but it still requires some careful
+ bootstrapping.
+
+
+
+ Your system's hardware architecture isn't supported
+ by GHC. This will be a more difficult port (though by
+ comparison perhaps not as difficult as porting
+ gcc).
+
+
+
+ Both ways require you to bootrap from intermediate
+ HC files: these are the stylised C files
+ generated by GHC when it compiles Haskell source. Basically
+ the idea is to take the HC files for GHC itself to the target
+ machine and compile them with gcc to get a
+ working GHC, and go from there.
+
+ The Building
+ Guide has all the details on how to bootstrap GHC on a
+ new platform.
+
+
+
+
+
+ Why doesn't GHC use shared libraries?
+
+ The subject of shared libraries has come up several
+ times in the past — take a look through the mailing-list
+ archives for some of the previous discussions. The upshot is
+ that shared libraries wouldn't really buy much unless you
+ really need to save the disk space: in all other
+ considerations, static linking comes out better.
+
+ Unfortunately GHC-compiled libraries are very tightly
+ coupled, which means it's unlikely you'd be able to swap out a
+ shared library for a newer version unless it was compiled with
+ exactly the same compiler and set of
+ libraries as the old version.
+
+
+
+
+ I can't get string gaps to work
+
+ If you're also using CPP, beware of the known pitfall
+ with string gaps mentioned in .
+
+
+
+
+ GHCi complains about missing symbols like
+ CC_LIST when loading a previously compiled .o
+ file.
+
+ This probably means the .o files in question were
+ compiled for profiling (with ). Workaround:
+ recompile them without profiling. We really ought to detect
+ this situation and give a proper error message.
+
+
+
+
+ Linking a program causes the following error on Linux:
+ /usr/bin/ld: cannot open -lgmp: No such file or
+ directory
+
+ The problem is that your system doesn't have the GMP
+ library installed. If this is a RedHat distribution, install
+ the RedHat-supplied gmp-devel package, and
+ the gmp package if you don't already have
+ it. There have been reports that installing the RedHat
+ packages also works for SuSE (SuSE don't supply a shared gmp
+ library).
+
+
+
+
+ I Can't run GHCi on Linux, because it complains about a
+ missing libreadline.so.3.
+
+ The "correct" fix for this problem is to install the
+ correct RPM for the particular flavour of Linux on your
+ machine. If this isn't an option, however, there is a hack
+ that might work: make a symbolic link from
+ libreadline.so.4 to
+ libreadline.so.3 in
+ /usr/lib. We tried this on a SuSE 7.1 box
+ and it seemed to work, but YMMV.
+
+
+
+
+ Solaris users may sometimes get link errors due to
+ libraries needed by GNU Readline.
+
+ We suggest you try linking in some combination of the
+ termcap, curses and
+ ncurses libraries, by giving
+ -ltermcap, -lcurses and
+ -lncurses respectively. If you encounter
+ this problem, we would appreciate feedback on it, since we
+ don't fully understand what's going on here.
+
+
+
+
+ When I try to start ghci (probably one I compiled myself)
+ it says ghc-5.02: not built for interactive
+ use
+
+ To build a working ghci, you need to build GHC 5.02 with
+ itself; the above message appears if you build it with 4.08.X,
+ for example. It'll still work fine for batch-mode
+ compilation, though. Note that you really must build with
+ exactly the same version of the compiler. Building 5.02 with
+ 5.00.2, for example, may or may not give a working interactive
+ system; it probably won't, and certainly isn't supported.
+ Note also that you can build 5.02 with any older compiler,
+ back to 4.08.1, if you don't want a working interactive
+ system; that's OK, and supported.
+
+
+
+
+ When I use a foreign function that takes or returns a
+ float, it gives the wrong answer, or crashes.
+
+ You should use the option to
+ bring the correct prototype into scope (see ).
+
+
+
+
+ My program that uses a really large heap crashes on
+ Windows.
+
+ For utterly horrible reasons, programs that use more
+ than 128Mb of heap won't work when compiled dynamically on
+ Windows (they should be fine statically compiled).
+
+
+
+
+ GHC doesn't like filenames containing
+ +.
+
+ Indeed not. You could change + to
+ p or plus.
+
+
+
+
+ When I open a FIFO (named pipe) and try to read from it, I
+ get EOF immediately.
+
+ This is a consequence of the fact that GHC opens the
+ FIFO in non-blocking mode. The behaviour varies from OS to
+ OS: on Linux and Solaris you can wait for a writer by doing an
+ explicit threadWaitRead on the file
+ descriptor (gotten from Posix.handleToFd)
+ before the first read, but this doesn't work on FreeBSD
+ (although rumour has it that recent versions of FreeBSD
+ changed the behavour to match other OSs). A workaround for
+ all systems is to open the FIFO for writing yourself, before
+ (or at the same time as) opening it for reading.
+
+
+
+
+ When I foreign import a function that
+ returns char or short, I
+ get garbage back.
+
+ This is a known bug in GHC versions prior to 5.02.2.
+ GHC doesn't mask out the more significant bits of the result.
+ It doesn't manifest with gcc 2.95, but apparently shows up
+ with g++ and gcc 3.0.
+
+
+
+
+
+
+
+
hunk ./ghc/docs/users_guide/intro.sgml 82
- This list is for GHC users to chat among
- themselves.
+ This list is for GHC users to chat among themselves.
+ If you have a specific question about GHC, please check the
+ FAQ first ().
hunk ./ghc/docs/users_guide/intro.sgml 244
- How do I tell if my bug has already been
- reported?
-
- Try searching the mailing list archives. The archives
- don't have a built-in search facility, but we find that How do I tell if I should report my bug?
+
+ Take a look at the FAQ () and , which will give you some guidance as to
+ whether the behaviour you're seeing is really a bug or
+ not.
+
+ If it is a bug, then it might have been reported before:
+ try searching the mailing list archives. The archives don't
+ have a built-in search facility, but we find that If in doubt, just report it.
hunk ./ghc/docs/users_guide/ug-book.sgml 21
+&faq;
+
hunk ./ghc/docs/users_guide/ug-ent.sgml 2
+
}