Could someone explain to me why this doesn't work

test l =
   hs
      where
         hs = map (\x -> [x]) [0..abs(l `div` hLen)]
         hLen   = length $ head hs

whereas this does

test l =
   hs
      where
         hs = map (\x -> [x]) (0:[1..abs(l `div` hLen)])
         hLen   = length $ head hs

I would have thought laziness would allow the compiler to know that hs would contain at least one element and therefore calculate hLen.

Dominic.