Instalei diagramas e parece estar lá, mas o GHCi não o encontra. Tentei adicionar a sandbox local à linha de comando (-package-db), mas ainda não tive sorte. Alguma sugestão?

   C:\Users\guthrie>
   C:\Users\guthrie>cabal install diagrams
    Resolving dependencies...
    All the requested packages are already installed:
   diagrams-1.2
   Use --reinstall if you want to reinstall anyway.

Eu encontro em:

  C:\Users\guthrie\.cabal-sandbox\i386-windows-ghc-7.6.3-packages.conf.d
        (diagrams-1.2, diagrams-contrib, -core, -lib, -svg) 

Mas executando: "cabal repl" ou usando a bandeira do GHC (i) "-package-db =…"Falha ao encontrá-lo:

C:\Users\guthrie>cabal repl
GHCi, version 7.6.3: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Prelude> :m + Diagrams.Prelude

<no location info>:
    Could not find module `Diagrams.Prelude'
   It is not a module in the current program, or in any known package.
Prelude>

Esclarecer; ignorando as invocações da cabala, usando o GHC / i diretamente e o programa diagramsDemo.hs:

--  http://projects.haskell.org/diagrams/doc/quickstart.html
--
import Diagrams.Prelude
import Diagrams.Backend.SVG.CmdLine

main = mainWith (circle 1 :: Diagram B R2)

Dá:

C:\Users\guthrie\Desktop\xFer\Graphics>ghc --make diagramsDemo.hs

diagramsDemo.hs:7:8:
    Could not find module `Diagrams.Backend.SVG.CmdLine'
    Use -v to see a list of the files searched for.

C:\Users\guthrie\Desktop\xFer\Graphics>ghc --make diagramsDemo.hs -package-db=C:\Users\guthrie\.cabal-sandbox\i386-windows-ghc-7.6.3-packages.conf.d

diagramsDemo.hs:7:8:
    Could not find module `Diagrams.Backend.SVG.CmdLine'
    Use -v to see a list of the files searched for.