I did an install of Diagrams, and all seemed fine.
>cabal install diagrams
Resolving dependencies...
All the requested packages are already installed: diagrams-1.2
Use --reinstall if you want to reinstall anyway.
But if I try to use it: import Diagrams.Prelude
Could not find module `Diagrams.Prelude'
Use -v to see a list of the files searched for.
And:
>ghc-pkg list diagrams
WARNING: there are broken packages.
Run 'ghc-pkg check' for more details.
e:/Plang/Haskell Platform\lib\package.conf.d:
(no packages)
C:\Users\guthrie\AppData\Roaming\ghc\i386-mingw32-7.8.3\package.conf.d:
(no packages)
(The broken packages are all old versions of things that have a good newer version installed.)
It seems to be installed in .cabal-sandbox, but that is not reported by ghc-pkg (?):
C:\Users\guthrie\.cabal-sandbox\i386-windows-ghc-7.8.3-packages.conf.d\Diagrams...
I understand that instead of GHCi I could use “cabal repl” which would add additional package library references to this to the path, but I want to use these installed libraries from other Haskell IDEs (Heat, Leksah).
I am not sure if this sandbox is a remnant for a previous cabal-install that would not work otherwise, or if the new cabal version (1.22) uses them automatically, or…
I found that using “cabal exec ghc” might solve this, but I tried it, and although putting in the explicit path myself worked, I didn't find the right usage for this:
-- Good:
ghc --make Program.hs -package-db=c:\users\name\.cabal-sandbox\i386-windows-ghc-7.8.3-packages.conf.d\
-- Fails:
cabal ghc --make Program.hs
Also current IDEs don’t have this option. Do I have to then add a command line option pointing to this directory ( -package-db= ) to all other tools that use GHC? and is this the right approach?
In general, IDEs and other tools which call cabal / GHC need to be aware of sandboxes, and behave a bit differently depending on whether or not there is a sandbox. I can't speak to Leksah, but for emacs, knowing the CLI way makes setting up the IDE easier.
The sandbox-aware equivalent of ghci is cabal repl.
The sandbox-aware equivalent of ghc-pkg is cabal sandbox hc-pkg.
It may be worth cabalizing the Diagram that you want to build. I know this seems overkill for a single Haskell file that only depends on diagrams-lib. I find it takes less time to create a .cabal file (or add an executable section to a common my-diagrams.cabal) than to figure out how to make all the tools (emacs haskell-mode, ghc-mod, hslint, GHC) pick up packages from a sandbox while building a non-cabalized file.