Lab 5

[BertLisser]

Ex 2 The following is okay

constraints :: Sudoku -> [Constraint]
constraints s = sortBy length3rd
    [(r,c, freeAtPositions s (r,c)) |
                       (r,c) <- openPositions s ]

but why not simplify

-- A slightly modified version of the example prune code.
prune :: (Row,Column,Value)
      -> [Constraint] -> Bool -> [Constraint]
prune _ [] isNRC = []
prune (r,c,v) ((x,y,zs):rest) isNRC
  | r == x = (x,y,zs\\[v]) : prune (r,c,v) rest isNRC
  | c == y = (x,y,zs\\[v]) : prune (r,c,v) rest isNRC
  | sameBlock (r,c) (x,y) =
        (x,y,zs\\[v]) : prune (r,c,v) rest isNRC
  | isNRC && nrcSameBlock (r,c) (x,y) =
      (x,y,zs\\[v]) : prune (r,c,v) rest isNRC
  | otherwise = (x,y,zs) : prune (r,c,v) rest isNRC

? I see you understand this, but you are on the half way.