If you install the following packages on Debian 9  like so
you should be able to compile Forest2D.
apt-get install liblua5.2-dev lua5.2 luarocks gcc make cmake git

# you may have to configure luarocks to use lua5.2 by compiling luarocks with this configuration
# (./configure --lua-version=5.2 --versioned-rocks-dir)

cd /tmp && git clone https://github.com/torch/paths
luarocks install paths/rocks/paths-scm-1.rockspec
cd /tmp && wget https://github.com/Tangent128/luasdl2/archive/v2.0.3-4.0.tar.gz
# Its important to download v2.0.3-4.0 of luasdl2 as the latest version fails to compile (for me at least).
tar xf v2.0.3-4.0.tar.gz && cd luasdl2-2.0.3-4.0 && cmake .
make install # as root of course
