看起来大部分构建都在工作，但实际安装失败。
仔细放置 echo 命令表明该命令是失败的：
install_pkg "cabal-install"
这是我收到的错误：
cleaning...
Linking Setup ...
Configuring cabal-install-1.17.0...
Building cabal-install-1.17.0...
Preprocessing library cabal-install-1.17.0...
[ 1 of 71] Compiling Distribution.Compat.FilePerms ( Distribution/Compat/FilePerms.hs, dist/build/Distribution/Compat/FilePerms.o )
[ 2 of 71] Compiling Distribution.Compat.Semaphore ( Distribution/Compat/Semaphore.hs, dist/build/Distribution/Compat/Semaphore.o )
Distribution/Compat/Semaphore.hs:12:26:
Module `Control.Exception' does not export `mask_'
Error during cabal-install bootstrap:
Building the cabal-install package failed
这是完整的成绩单：
Checking installed packages for ghc-6.12.3...
Cabal is already installed and the version is ok.
transformers is already installed and the version is ok.
mtl is already installed and the version is ok.
deepseq is already installed and the version is ok.
text is already installed and the version is ok.
parsec is already installed and the version is ok.
network is already installed and the version is ok.
time is already installed and the version is ok.
HTTP is already installed and the version is ok.
zlib is already installed and the version is ok.
random is already installed and the version is ok.
stm is already installed and the version is ok.
===========================================
cleaning...
Linking Setup ...
Configuring cabal-install-1.17.0...
Building cabal-install-1.17.0...
Preprocessing library cabal-install-1.17.0...
[ 1 of 71] Compiling Distribution.Compat.FilePerms ( Distribution/Compat/FilePerms.hs, dist/build/Distribution/Compat/FilePerms.o )
[ 2 of 71] Compiling Distribution.Compat.Semaphore ( Distribution/Compat/Semaphore.hs, dist/build/Distribution/Compat/Semaphore.o )
Distribution/Compat/Semaphore.hs:12:26:
Module `Control.Exception' does not export `mask_'
Error during cabal-install bootstrap:
Building the cabal-install package failed