Haskell List Comprehension -

I get the "not missing: x" error when it happens ...

  Blanks: Sudoku - & gt; [Pos] Spaces (Sudoku su) = [FST X | X & LT; - POSSED | IsBlank (snd x)] Where is nothing mismatched = true is black_ = false posz = zip ixPos (concat su) ixPos = zip ixRows ixCols ixCols = concat (9 [0..8] repeat) ixRows = [floor (X / 9). X & lt; - [0..81]]  

However, if I compile the security of 2: ND line GHCI without any errors.

Can you help me understand what I am doing?

Try [fst x | X & LT; - POSASSAD, ISBN (sd)]