Inner loop for finding all the ways to add up to a number

addition_loop.hs

loop counter runningTotal accumulator = do 
  current <- pool
  
  case accumulator of
    []            -> guard True
    (previous:_)  -> guard (current < previous)
    
  guard (current + runningTotal <= target)
    
  loop (counter-1) (runningTotal+current) (current:accumulator)