[Haskell-cafe] ghc6.8: hiding uninstalled package?

Magnus Therning magnus at therning.org
Thu Jan 17 13:24:00 EST 2008

On 1/17/08, Albert Y. C. Lai <trebla at vex.net> wrote:
> Magnus Therning wrote:
> > This might seem like a silly question, but what's the reasoning behind
> > the following behaviour?
> >
> > % ghc-pkg list dataenc
> > /usr/lib/ghc-6.8.2/package.conf:
> > % ghc --make -hide-package dataenc -isrc UT.hs
> > ghc-6.8.2 : unknown package: dataenc
> >
> > Hiding an uninstalled package doesn't seem to warrant failing
> compilation!
> "I cannot find it, therefore I cannot hide it"? XD
> The following is fairly widely accepted behaviour:
> $ rm phd-thsies
> rm: cannot remove `phd-thsies': No such file or directory
> If a file is absent and you want it absent, is that an error?
> (Now you might get into a long thread debating whether deletion is
> analogous to hiding...)
> If I want to hide or delete something, and the computer can't find that
> something, it may be because I have a typo. If the computer remains
> silent about it, I fail to hide or delete the true thing. I want to
> delete phd-thesis, but I typed phd-thsies, and I appreciate the error
> report. If I fail to delete phd-thesis, at worst more people read it and
> be enlightened :) but if I fail to hide a package and I don't know about
> it, the ensuing problems will be much more mysterious.

Fair enough.  I stumbled on this behaviour because I was writing a makefile
for my unit/quickcheck tests.  I need to make sure that the correct module
is used, hence I need to hide it if it's installed.  I ended up with the
following in order to work around the issue:

ifeq (,$(shell ghc-pkg list dataenc | grep dataenc))
GHCOPTS = -fhpc -isrc
GHCOPTS = -fhpc -hide-package dataenc -isrc

% : %.hs
        ghc --make $(GHCOPTS) $<

Is there a better way to do it?

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