Programming for a mathematician?

I have started studying Haskell. I expect the type system and monads to be the most interesting things to learn (I know common lisp and have already seen many cool features). Though the days of general programming are long gone. I am interested in writing math apps though. Should I continue learning Haskell or should I start studying Mathematica (or some other alternative like matlab/maple) instead?

What do you mean by `math program' ?  Do you mean trivialities like automated applications of Cramer's rule - larger versions of the QUADRATC program everyone wrote on their TI-8X back in the day? Programs which do not use an abnormal amount of higher math but have math-related content, like a `Lemma of the day' reminder?  Distributed prime-checkers on the GPU?

It really depends. If you want to encode theorems into programs, you want Coq, although you could continue with Haskell. If you want to do stuff like FFT at usable speeds, you want OCaml (in which FFTW is implemented), C, or even trusty Fortran.  If you want to do anything involving large scale brute force, you'll want to experiment with CUDA and OpenCL.