One Billion Row challenge in Hs

This version now runs in 29s on my computer, 8s less than the previous version. And RAM usage went down to 60MB (-15GB).

% hyperfine -w 1 -r 5  './exe-exe > ../solution.txt'
Benchmark 1: ./exe-exe > ../solution.txt
  Time (mean ± σ):     28.535 s ±  0.023 s    [User: 25.609 s, System: 2.818 s]
  Range (min … max):   28.505 s … 28.556 s    5 runs