How to reset Haskell package cache - haskell

Question

Deciding to learn Haskell, installed ghc on OS X via Homebrew (web binaries weren't downloading at the time).
All great, following along with Learn You a Haskell, but then decided to install some packages and see how things run.
cabal install clckwrks-cli was running fine until...
Public internet craps out half-way through install/build of a few projects.
Now, none of those programs will reinstall and in the case of clckwrks-cli, I get the following error:
$ cabal install clckwrks-cli --reinstall --force-reinstalls
Resolving dependencies...
Failed to install cipher-aes-0.2.6
Failed to install cipher-rc4-0.1.4
Failed to install cookie-0.4.0.1
Failed to install crypto-numbers-0.2.3
Configuring happstack-hsp-7.2.4...
Building happstack-hsp-7.2.4...
Preprocessing library happstack-hsp-7.2.4...
ghc: could not execute: hsx2hs
Failed to install happstack-hsp-7.2.4
Failed to install lifted-base-0.2.2.0
Failed to install publicsuffixlist-0.1
Failed to install pwstore-purehaskell-2.1.1
Configuring reform-hsp-0.2.4...
Building reform-hsp-0.2.4...
Preprocessing library reform-hsp-0.2.4...
ghc: could not execute: hsx2hs
Failed to install reform-hsp-0.2.4
Failed to install web-plugins-0.2.5
Failed to install wl-pprint-text-1.1.0.2
Failed to install xml-types-0.3.4
cabal: Error: some packages failed to install:
attoparsec-conduit-1.0.1.2 depends on lifted-base-0.2.2.0 which failed to
install.
authenticate-1.3.2.6 depends on xml-types-0.3.4 which failed to install.
blaze-builder-conduit-1.0.0 depends on lifted-base-0.2.2.0 which failed to
install.
cipher-aes-0.2.6 failed while unpacking the package. The exception was:
user error (data is not in tar format)
cipher-rc4-0.1.4 failed while unpacking the package. The exception was:
user error (data is not in tar format)
clckwrks-0.21.1 depends on xml-types-0.3.4 which failed to install.
clckwrks-cli-0.2.10 depends on xml-types-0.3.4 which failed to install.
conduit-1.0.14 depends on lifted-base-0.2.2.0 which failed to install.
cookie-0.4.0.1 failed while unpacking the package. The exception was:
user error (data is not in tar format)
cprng-aes-0.5.2 depends on cipher-aes-0.2.6 which failed to install.
crypto-numbers-0.2.3 failed while unpacking the package. The exception was:
user error (data is not in tar format)
crypto-pubkey-0.2.4 depends on crypto-numbers-0.2.3 which failed to install.
fb-0.14.11 depends on publicsuffixlist-0.1 which failed to install.
happstack-authenticate-0.10.10 depends on xml-types-0.3.4 which failed to
install.
happstack-hsp-7.2.4 failed during the building phase. The exception was:
ExitFailure 1
hsx-jmacro-7.3.4 depends on wl-pprint-text-1.1.0.2 which failed to install.
http-conduit-1.9.6 depends on publicsuffixlist-0.1 which failed to install.
jmacro-0.6.8 depends on wl-pprint-text-1.1.0.2 which failed to install.
lifted-base-0.2.2.0 failed while unpacking the package. The exception was:
user error (data is not in tar format)
monad-logger-0.3.4.0 depends on lifted-base-0.2.2.0 which failed to install.
publicsuffixlist-0.1 failed while unpacking the package. The exception was:
user error (data is not in tar format)
pwstore-purehaskell-2.1.1 failed while unpacking the package. The exception
was:
user error (data is not in tar format)
reform-hsp-0.2.4 failed during the building phase. The exception was:
ExitFailure 1
resourcet-0.4.10 depends on lifted-base-0.2.2.0 which failed to install.
tls-1.1.5 depends on crypto-numbers-0.2.3 which failed to install.
tls-extra-0.6.6 depends on crypto-numbers-0.2.3 which failed to install.
web-plugins-0.2.5 failed while unpacking the package. The exception was:
user error (data is not in tar format)
wl-pprint-text-1.1.0.2 failed while unpacking the package. The exception was:
user error (data is not in tar format)
xml-conduit-1.1.0.9 depends on xml-types-0.3.4 which failed to install.
xml-types-0.3.4 failed while unpacking the package. The exception was:
user error (data is not in tar format)
zlib-conduit-1.0.0 depends on lifted-base-0.2.2.0 which failed to install.
Same issue with a few other projects that suffered same network outage mid-install.
Loving the language so far, NOT the package management :(

Answer 1

Cabal sandboxes are frequently recommended for development but work well for trying out some package quickly. If anything goes wrong they are easily disposable and don't affect any other packages you have already installed. Here is what I would do to try out clckwrks-cli (BTW, if you want to just try out any package you might to choose another package with less dependencies).
$ cd /path/to/sandboxes
$ cabal get clckwrks-cli
$ cd clckwrks-cli-<version>
$ cabal sandbox init
$ cabal install --only-dependencies -j<N> # N is the number of CPU cores
At this point you can type cabal run to run the executable installed by the package (which it'll probably be at ./dist/build/bin/), cabal test for running tests, or cabal repl in order to run a ghci session with the sandboxes packages available.
If anything goes wrong you can revert back the sandbox by typing cabal sandbox delete and cabal clean. When you are done you can safely remove the sandbox without affecting other packages.

Answer 2

Here is what worked for me in the past
For a package $f, do
ghc-pkg.exe unregister --global --force $f
ghc-pkg.exe recache
According to its documentation, ghc-pkg.exe unregister "unregisters a package" and recache "regenerate the package database cache". --global needs to be used if the package in question was installed in system directories.
In case the database is severely damaged, I would delete the user or system cabal directory and reinstall packages that I had. I usually do this by cabal install one or several of the application libraries that I use, and let cabal reinstall the dependencies. Note: the cabal directory depends on the OS and version of GHC.
ghc-pkg unregister --force clckwrks-cli

Answer 3

I was having trouble with unordered-containers-0.2.5.1 and deleting the file:
~/.cabal/packages/hackage.haskell.org/unordered-containers/0.2.5.1/unordered-containers-0.2.5.1.tar.gz
fixed the problem for me. (i.e. the error cabal: data is not in tar format)