It's extremely debatable that Haskell is compute-oriented. I know that Haskell people like to talk about doing numerical computing in Haskell, but in reality it does not seem to be a thing. No one has ever used Haskell to implement large scale scientific computations on supercomputers, for example.
This particular example appears to be an implementation of a 'Computer algebra system', which seems to be a type of symbolic computing rather than numerical computing.
> The only systems which have supported compute-oriented composable parallelism like this are Cilk and TBB
Because it isn’t true. Haskell is an example of why it isn’t true.