Lab 5

[BertLisser]

subgridInjective :: Sudoku -> (Row,Column) -> Bool
subgridInjective s (r,c) = injective vs where
   vs = filter (/= 0) (subGrid s (r,c))

consistent :: Sudoku -> Bool
consistent s = and $
               [ rowInjective s r |  r <- positions ]
                ++
               [ colInjective s c |  c <- positions ]
                ++
               [ subgridInjective s (r,c) |
                    r <- [1,4,7], c <- [1,4,7]]

The call of function subgridSecondInjective is missing in consistent.
Ex. 2
The following code is Okay

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

but why not refactor the code

prune :: (Row,Column,Value)
      -> [Constraint] -> [Constraint]
prune _ [] = []
prune (r,c,v) ((x,y,zs):rest)
  | r == x = (x,y,zs\\[v]) : prune (r,c,v) rest
  | c == y = (x,y,zs\\[v]) : prune (r,c,v) rest
  | sameblock (r,c) (x,y) =
        (x,y,zs\\[v]) : prune (r,c,v) rest
  | sameblock2 (r,c) (x,y) =
        (x,y,zs\\[v]) : prune (r,c,v) rest
  | otherwise = (x,y,zs) : prune (r,c,v) rest

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

Exercise 4
Good. Only unnecessary complicated code.

ex4_21 :: Int -> IO ()
ex4_21 n = ex4_22 n False 0 emptyN emptyN emptyN

ex4_22 :: Int -> Bool -> Int -> Node -> Node -> Node -> IO ()
ex4_22 _ False 1000 _ _ _ = do
  print("No sudoku found")
ex4_22 n False c _ _ _ = do
  print("Try")
  print(show c)
  print("/1000")
  r <- genRandomSudoku
  bs <- randomize [0..8]
  let x = eraseBs r (take n bs)
  temp <- genProblem x
  ismin <- isMinimal temp
  ex4_22 n ismin (c+1) r x temp
ex4_22 n True c r x temp = do
  showNode r
  showNode x
  showNode temp

Exercise 5
The question was to generate NRC sudokos's without empty blocks. Thus the code can then be much simpler. But the remark is correct.