Packages

To avoid compiling everything from source all the time, there is a notion of a precompiled package. A package is simply a set of modules that are compiled together and that can then be installed in a known place (typically ~/.mcabal/mhs-VERSION/packages/). Packages can depend on already installed packages.

There is a search path for installed packages, controlled by the -a flag.

There is no need for any extra flags to mhs to use installed packages, they are all visible at all times. When compiling to a binary, only the used parts of a package will be included in the binary.

Compiling a package

To compile a package, use the command mhs -Ppackage-name.pkg modules... where modules... are all the modules you wish to expose from the package. If other modules are needed, they will automatically be included in the package. You typically also want to use the -o flag to give the package a sensible name.

Installing a package

To install a package, use the command mhs -Q package-name.pkg [install-dir]. If the install-dir is left out, the package is installed in the default place.

MicroCabal (mcabal)

Normally a package is downloaded from Hackage and it will have a .cabal file that describes the package contents. To install a downloaded package, simply do mcabal install. The mcabal program is included in the MicroHs download. You can also do mcabal install PKG to download and install a package.

Installed package organization

The packages are typically installed in ~/.mcabal/ and it has the following layout:

• .mcabal/bin/ installed binaries, initially mhs, cpphs, and mcabal
• .mcabal/mhs-VER/ installed files for the given mhs version
• .mcabal/mhs-VER/packages/ for each library package a PKG.pkg file (the binary blob for the package) and also (maybe) a directory PKG/ that contains data/, include/, and cbits/ for the package.
• .mcabal/.../MODULE.txt a file for each installed module, it contains the name of the package that contains that module.

For example, after installing mhs version 0.10.5.0 we will have something like this:

.mcabal/
        bin/cpphs
            mcabal
            mhs
        mhs-0.10.5.0/Control/Applicative.txt   -- contains "base-0.10.5.0.pkg"
                             ...
                             Monad/Fail.txt    -- contains "base-0.10.5.0.pkg"
                                   ...
                             ...
                     Data/
                     ...
                     Prelude.txt               -- contains "base-0.10.5.0.pkg"
                     packages/base-0.10.5.0.pkg
                              mhs-0.10.5.0/data/src/runtime/eval.c
                                                            ...

A (maybe) short-coming of the package system is that there can only be one version of a package installed at a time. If you need multiple versions, you have to use different directories for them and use -a to control it. There are absolutely no checks for consistency among packages. There is also no compatibility between packages compiled with different versions of the compiler.

Hackage

Hackage is full of great packages, unfortunately most of them contain some GHC specific code. Some compile, most don't. Some have replacement, most don't. Here's a summary of the current state:

Packages included with the compiler

• array some of the functionality
• base most of what GHC has in base
• bytestring some of the functionality
• deepseq some of the functionality
• directory some of the functionality
• hashable a little of the functionality
• integer-logarithms
• process very little of the functionality
• stm most of the functionality
• text some of the functionality

Package status

You can find the status for various packages. If a package is not in the list it just means that nobody has reported success of failure with the package. Please do so.