FP is a fertile topic for CS research in part because writing good compilers for FP languages is hard and poses lots of challenging questions for people to try to answer.
Most really low level code generation and parsing research etc. will apply across the board or at least cover a wide range of type of languages (e.g. register allocation, instruction selection).
But consider type theory - a language like Haskell providers a lot wider scope for research in that area than e.g. C. Or garbage collection - admittedly that's more widely applicable, but many FP languages throw an extra factor into the mix with immutable variables. Etc.
But there's certainly other PL research as well. E.g. all the work that's gone into Javascript compilers in the last few years. Trace trees came out of work done on a JVM for example.
Most really low level code generation and parsing research etc. will apply across the board or at least cover a wide range of type of languages (e.g. register allocation, instruction selection).
But consider type theory - a language like Haskell providers a lot wider scope for research in that area than e.g. C. Or garbage collection - admittedly that's more widely applicable, but many FP languages throw an extra factor into the mix with immutable variables. Etc.
But there's certainly other PL research as well. E.g. all the work that's gone into Javascript compilers in the last few years. Trace trees came out of work done on a JVM for example.