Understanding directory structure of ghc installation

[Simon Marlow]

Brian Hulley wrote:
> Hi -
> I've just downloaded and installed Edison using Cabal.
> However I now see that Edison seems to have been already installed with 
> the ghc 6.4.2 installation, even though there's no mention of Edison in 
> /doc/html/libraries/index.html, because there are old Edison .hi files in
> 
>    ghc-6.4.2/hslibs-imports/data
> 
> whereas the Cabal install process copied newly built Edison files to
>      C:\Program Files\Haskell\EdisonAPI-1.2\ghc-6.4.2\Data
> and
>      C:\Program Files\Haskell\EdisonCore-1.2\ghc-6.4.2\Data
> 
> I was about to just delete the old .hi files from the 
> hslibs-imports/data directory, but then I noticed there are a few .hi 
> files there for Set and FiniteMap, even though there are also .hi files 
> (though of different sizes) for Set and FiniteMap stored in the 
> imports/data directory as well.
> 
> So my question is: how to understand all this? Why are there different 
> copies of Set.hi which have different sizes, but in the same 
> installation, and which one does ghc use when I use import Data.Set in a 
> program?

Everything in hslibs-imports is for the old "hslibs" libraries.  These 
are the non-hierarchical libraries that came with GHC < 5.04 and are 
still provided for backwards compatibility, although they will be 
removed in GHC 6.6.

The documentation for the old libraries is here: 
http://www.haskell.org/ghc/docs/latest/html/hslibs/index.html

(which is linked from the GHC documentation page, "(Old) Haskell 
Libraries").

> Also, what does .p_hi mean? (The new build of Edison only creates .hi 
> files not .p_hi files but all the ghc-6.4.2 modules have both .hi and 
> .p_hi files)

the .p_hi are the interface files for the profiling versions of these 
modules.  If you configure with --enable-library-profiling you will get 
profiling libs for a Cabal package too.

> (It would also be interesting to know where Cabal gets the information 
> from to configure a package, and where the package database is stored...)

Cabal needs to collect various information: what GHC version you have, 
what versions of packages are available, etc.

The ghc-pkg command is the interface to the package database.  It will 
tell you where your package database is stored ("ghc-pkg list").

Cheers,
	Simon