Is it doable to employ functional programming in implementing intraoperation parallelism in Postgres?

For my undergraduate final year project, I want to study functional programming and intraoperation parallelism in DBMS. Specifically, I am going to investigate into whether FP could be useful for implementing operations as selection, projection, and join (these operations could easily be parallelized and FP's referential transparency could give some benefits here).

I figured that Postgres is a good DBMS to study since it makes use of intraoperation parallelism. However, Postgres is written in C. Is there a way to achieve what I have in mind? Is it doable given how the code is structured? 

Regards,