lookup n = case n of
  1 -> "A"
  2 -> "B"
  3 -> "C"
  _ -> "X"

-- Knapsack!  But, first, we do subsets...

subsets [] = [[]]
subsets (x:xs) = subsWithX ++ subsWithoutX
  where
    subsWithoutX = subsets xs
    subsWithX = map (x:) subsWithoutX

-- Now, knapsack.  List of three-tuples, (name, value, weight)

value sub = sum (map (\(_,val,_)->val) sub)
weight sub = sum (map (\(_,_,weight)->weight) sub)

knapsack items limit = ...
  where
    -- options is a list of the sets of items that will fit
    options = filter (\set->weight set<=limit) (subsets items)