Re: [Haskell-beginners] Module import problem

On Sun, Sep 28, 2008 at 7:33 PM, Christian Cheng wrote:

On Mon, Sep 29, 2008 at 12:20 AM, Casey Rodarmor wrote:

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On Sun, Sep 28, 2008 at 6:08 PM, Chry Cheng wrote:

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"Casey Rodarmor" writes:

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Hi there!

I have a problem with importing a module I'd like to use.

My working directory, ~/proj, contains: ./Haskore -- a folder containing a version of haskore, this music thingy ./test.hs -- random stuff using haskore

The main file in ~/proj/Haskore is ~/proj/Haskore/Haskore.hs, which contains the following module declaration:

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module Haskore(module HaskoreLoader) where import HaskoreLoader

I've tried to put all the following in ~/proj/test.hs, with no luck:

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import Haskore -- Could not find module `Haskore': import Haskore.Haskore -- file name does not match module name `Haskore'

Am I doing something wrong? Is there a way to place a module in an arbitrary directory, without having to modify it?

Thanks so much for your help!

Best, Casey Rodarmor _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners

You have to tell GHC where to find Haskore. To do this, call ghc with the i option:

ghc -iHaskore/

then, import using:

import Haskore

Hi Chry,

Thanks for the answer, everything works now :-)

I must admit, I'm a little disappointed if that's the only way to get it to work. On the surface of things, I don't see why one can't just put a Module in some/arbitrary/directory, and then import it as some.arbitrary.directory.Module. The need to use a flag on the command line seems a little unnecessary.

I beg to differ. I don't think it's reasonable to expect the compiler to figure out on its own where we have stashed additional classes. Other programming languages have a similar requirement. For Java, it's the class path (e.g., javac -classpath Haskore); C/C++, the include directories (IIRC, gcc -I Haskore), etc.

I was fooling around with Java, and you're totally right, the module itself must know about its full name, so you can't have a java file which declares itself as "package Foo.Thingy;" in Bar/Foo/Thingy.java, and then do an "import Bar.Foo.Thingy". It is worth noting that in C and C++, a double-quoted #include will search relative to the current source file. Even though that doesn't have anything to do with locating the object file that you'll probably want to link in later... The comparison I was thinking of was with python, where a module can be placed in an arbitrary directory, and then accessed using a relative path. If I have 'stuff.py' that contains class 'Foo', I can move it to 'hello/module/stuff.py', and then import it is hello.module.stuff. A python module doesn't need to know where it lives. I often find myself working on computers where I don't have administrative privileges, which means I might not be able to install libraries in the 'right' places. This approach also makes it simple to create self-contained projects that can easily be moved from machine to machine, where only the local directory structure is important. Would there be any downside to this in haskell?

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Can anyone give a little insight into why this decision was made?

Best, Casey _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners