[Haskell-cafe] One problem with Cabal-install and dependencies

[Michael Lazarev]

Hi, everybody!

I think there's either an error in cabal-install, or I don't have an
idea on haskell packages.
I tried to install one particular library that depends on
containers-0.2.0.1 and got the following error:

Data/IntMap.hs:182:7:
    Could not find module `Data.Data':
      It is a member of the hidden package `base'.
      Perhaps you need to add `base' to the build-depends in your .cabal file.
      Use -v to see a list of the files searched for.

Then I tried to install containers-0.2.0.1 separately, andin the
process of the struggle I found that issuing the following command in
containers-0.2.0.1 directory:
~/.cabal/bin/cabal install --constraint="base >= 4" -v
... prints this:

Resolving dependencies...
selecting containers-0.2.0.1 (hackage)
selecting array-0.3.0.1 (installed or hackage) and discarding array-0.1.0.0,
0.2.0.0 and 0.3.0.0
selecting base-3.0.3.2 (installed) and 4.2.0.1 (installed) and discarding
syb-0.1.0.0, 0.1.0.1, 0.1.0.2, 0.1.0.3, 0.2 and 0.2.1
selecting ffi-1.0 (installed)
selecting ghc-prim-0.2.0.0 (installed)
selecting integer-gmp-0.2.0.1 (installed)
selecting rts-1.0 (installed)
selecting syb-0.1.0.2 (installed)
In order, the following would be installed:
containers-0.2.0.1 (new version)
Configuring containers-0.2.0.1...
Dependency array ==0.3.0.1: using array-0.3.0.1
Dependency base ==3.0.3.2: using base-3.0.3.2

And proceeds to building the library:

/usr/local/bin/ghc --make -package-name containers-0.2.0.1
-hide-all-packages -fbuilding-cabal-package -i -idist/build -i.
-idist/build/autogen -Idist/build/autogen -Idist/build -Iinclude
-optP-include -optPdist/build/autogen/cabal_macros.h -odir dist/build
-hidir dist/build -stubdir dist/build -package-id
array-0.3.0.1-fb28b07fd38a6011f4f73844e0d8281f -package-id
base-3.0.3.2-260693a92016991a03206b5a55f6a411 -O -XDeriveDataTypeable
-XMagicHash -XRank2Types -XCPP Data.Graph Data.IntMap Data.IntSet
Data.Map Data.Sequence Data.Set Data.Tree

where, as you see, it really uses base-3.0.3.2, and thus fails.

So, my qusetion is, whether I'm doing something wrong, or there are
really two errors:
1) cabal-install makes a wrong choice for dependency version
2) cabal-install does not respect the constraint, and proceeds to
building the library without any warning