Hi,

> * gnu/packages/haskell-apps.scm (microcabal): New variable.

I’m using a slightly modified patch (see attachment), but `mcabal`
cannot build any packages. It seems that it ignores the MHSDIR environment
variable:

    mcabal build fail
    mcabal: Build package fail
    mcabal: Building in /home/lars/.mcabal/packages/fail-4.9.0.0
    mcabal: Building library fail
    mhs: error: no location: Module not found: Mhs.Builtin
    search path=[".","dist-mcabal/autogen"]
    package path=["."]
    mhs: error: callCommand: failed 256, "mhs -Pfail-4.9.0.0 -ofail-4.9.0.0.pkg -i -i. -idist-mcabal/autogen '-DVERSION_base=\"4.19.1.0\"' '-DMIN_VERSION_base(x,y,z)=((x)<4||(x)==4&&(y)<19||(x)==4&&(y)==19&&(z)<=1)' -a. Control.Monad.Fail"

Looking at the MicroCabal sources mcabal might be expecting mhs to be
installed as an “mcabal package”?

Lars