round

Prelude> round 0.5
0
Prelude> round 1.5
2
Prelude> round 2.5
2
Prelude> round 3.5
4

WHAT THE FUCK

It looks like it's fracked up to me. Either your rounding should be a ceiling or floor function, but not both as it seems with round 2.5 and round 3.5 to have both features. This can be fixed in the return statement, btw.