Found at dcu-impl as git submodule.
This should mean that it is cloned when this rulesforNMT repository is cloned.
If not, try
git submodule update --init --recursive
They don't document their dependencies; here are those I've had to install:
pip install theano
This installs numpy and scipy as well.
Regardless of the implementation of constrained decoding that we choose, there's likely room to learn from DCU's implementation.
Their NMT classes implement three generation methods:
generate()
generate_constrained()
continue_constrained()
...more to come.