Bit of a plug, I've written something like this except that it doesn't work via GHC and instead outputs source code (which means the gensyms aren't very safe...)

I'm not working on it anymore (unfortunately never really got over the static typing) but it should run and might be of interest: https://github.com/aliclark/hasp http://www-student.cs.york.ac.uk/~anc505/code/hasp/hasp.html