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Building GHC: The tools
After getting to know package databases we are going to look into the set of tools that are used when building the Glasgow Haskell Compiler.
alex & happy
alex is a tool to generate lexical analysers in Haskell, and as such can turn =.x= files into =.hs= files. happy is a parser generator, which can turn =.y= files into =.hs= files.
ghc-pkg
We saw during getting to know package databases. It is the command line interface to the package databases.
ghc-cabal
While cabal comes with the Cabal library and the cabal command line
tool in the cabal-install package. The build system needs an easy way
to just extract values from =.cabal= files and add some customizations
to configuring, copying, and registering packages via cabal. This is
what ghc-cabal is for. It produces the package-data.mk file, which
is a Makefile that contains information from the =.cabal= file, such as
it’s Haskell Sources, C Sources, … and as such provides the Make based
build system with sufficient information to build all the libraries.
Yes, we do not use cabal to build GHC.
deriveConstants
This utility is used during the build process to generate header files containing constant values (word sizes, …) of the target platform and when the compiler is built those are included to provide those target specific information.
hsc2hs
When binding to C libraries, the process can be quite tedious and
hsc2hs tries to make this a bit easier. It is also used quite a lot
outside of GHC itself. It even has its own
GHC
User’s Guide entry.
genapply & genprimopcode
GHCs runtime system needs to apply functions of various arities when
evaluating a program. genapply produces the AutoApply.cmm file which
is part of the rts package. The AutoApply.cmm file defines the
standard closures used to represent application of functions of various
artities.
Functions that can not be implement in Haskell directly are called
Primitive Operations (PrimOps) while these functions are provided
natively by GHC, the genprimopcode utility uses a highlevel
description of the PrimOps in the compiler/prelude/primops.txt.pp and
produces the necessary plumbing around them: header files, curried
wrappers, haddock information.
touchy
While unix systems have the touch command. Windows does not. As GHC
uses touch during building and compilation of Haskell files, touchy
is required on Windows as a substitute.
unlit
As GHC has support for Literate Haskell, it needs to be able to extract
the Haskell source from a =.lhs= source file. unlit is the filter that
can stirp the literate part out of a =.lhs= file and just leave
the =.hs= part.
compareSizes
When comparing two ghc builds, it can be of interest to see whether or
not the file size of haskell interface files (.hi) or objects (.o)
has increased or decreased. As such the compareSizes utility is not
essential to build GHC, but useful when trying to gauge what effect a
change has on interface and object file sizes.
hp2ps
The hp2ps tool is also widely used. It turns a heap profile generated
by GHC into a (hopefully) easier to undertand graphical representation.
ghctags
vim and emacs can read so called TAGS files, which provide an
index to source-code definitions of function, variables, and other
points of interest.
ghctags is capable of generating such a file for Haskell sources. As
such it is also a not an essential utility to build GHC.
hpc
The hpc tool can be used to generate code coverage reports for Haskell
code. It even has it’s own
page on the haskell
wiki.
In conclusion I hope this was somewhat informative. And while not all tools are strictly used to build GHC. I believe this covers all the utilities that are part of the GHC source tree.