test +RTS -stest1fs.stat 
566,400,800 bytes allocated in the heap
8,394,100,944 bytes copied during GC (scavenged)
     37,008 bytes copied during GC (not scavenged)
 42,578,884 bytes maximum residency (7 sample(s))

       1042 collections in generation 0 ( 95.94s)
          7 collections in generation 1 (  0.46s)

         84 Mb total memory in use

  INIT  time    0.03s  (  0.00s elapsed)
  MUT   time    2.83s  (  2.82s elapsed)
  GC    time   96.40s  ( 96.34s elapsed)
  EXIT  time    0.00s  (  0.00s elapsed)
  Total time   99.26s  ( 99.16s elapsed)

  %GC time      97.1%  (97.2% elapsed)

  Alloc rate    197,765,642 bytes per MUT second

  Productivity   2.9% of total user, 2.9% of total elapsed