There are two possibilities to install lhs2TeX:

(A) Using Cabal.
(B) Classic configure/make.

=====================================================================

(A) Using Cabal to install lhs2TeX (preferred):

This requires Cabal 1.6 or later. The process is then as usual:

cabal install

if you have cabal-install (included in the Haskell Platform) or

runghc Setup configure
runghc Setup build
runghc Setup install

The third step requires write access to the installation location and
the LaTeX filename database.

=====================================================================

(B) configure/make (might be removed in the future):

The following instructions apply to Unix-like environments.  However,
lhs2TeX does run on Windows systems, too. (If you would like to add
installation instructions or facilitate the installation procedure for
Windows systems, please contact the authors.)

Unpack the archive. Assume that it has been unpacked into directory
"/somewhere". Then say

cd /somewhere/lhs2TeX-1.21
./configure
make
make install

You might need administrator permissions to perform the "make install"
step. Alternatively, you can select your own installation location by
passing the "--prefix" argument to @configure@:

./configure --prefix=/my/local/programs

With lhs2TeX come a couple of library files (containing basic
lhs2TeX formatting directives) that need to be found by the
lhs2TeX binary. The default search path is as follows:

.
{HOME}/lhs2tex-1.21//
{HOME}/lhs2tex//
{HOME}/lhs2TeX//
{HOME}/.lhs2tex-1.21//
{HOME}/.lhs2tex//
{HOME}/.lhs2TeX//
{LHS2TEX}//
/usr/local/share/lhs2tex-1.21//
/usr/local/share/lhs2tex-1.21//
/usr/local/lib/lhs2tex-1.21//
/usr/share/lhs2tex-1.21//
/usr/lib/lhs2tex-1.21//
/usr/local/share/lhs2tex//
/usr/local/lib/lhs2tex//
/usr/share/lhs2tex//
/usr/lib/lhs2tex//
/usr/local/share/lhs2TeX//
/usr/local/lib/lhs2TeX//
/usr/share/lhs2TeX//
/usr/lib/lhs2TeX//

Here, {HOME} and {LHS2TEX} denote the current values of these two
environment variables HOME and LHS2TEX. The double slash at the end of
each dir means that subdirectories are also scanned. If lhs2TeX is
installed to a non-standard path, you might want to set the
environment variable "LHS2TEX" to point to the directory where
"lhs2TeX.fmt" and the other library files have been installed to.

IMPORTANT:
To be able to use ``poly'' style, the two LaTeX 
packages "polytable.sty" and "lazylist.sty" are required!

Both are included in the lhs2TeX distribution (they are not part of
standard LaTeX distributions, although they are available from
CTAN), and are usually installed during the normal procedure. The
configure script will determine whether a suitably recent version of
polytable is installed on your system, and if necessary, install
both "polytable.sty" and "lazylist.sty" to your TeX system. If this
is not desired or fails (because the script cannot detect your TeX
installation properly), the installation of these files can be
disabled by passing the option "--disable-polytable" to
"configure". In this case, the two files must be manually installed to
a location where your TeX distribution will find them.  Assuming
that you have a local TeX tree at "/usr/local/share/texmf", this can
usually be avhieved by placing the files in the directory
"/usr/local/share/texmf/tex/latex/polytable" and subsequently running

mktexlsr 

to update the TeX filename database.