Rational sequence

[Simon Peyton-Jones]

| Since I suppose you also want to receive constructive suggestions,
| I'd suggest to remove some instance definitions from the
| report.=20

I definitely can't do that at this stage.  I have never liked
Float/Double/Ratio being in Enum, but there is no possibility of
removing them now.  A year or two ago, maybe.

The task now is see a local optimum, not a global one.  We're in the
low-temperature phase of annealing.

Simon