I've created a:
newType Board = Board (Array (Int, Int) Life)
, where
data Life = Alive|Dead
Im trying to make a function to save the board to a String by pattern matching:
showBoard:: Config -> String
showBoard Board(array ((0, 0), (w, h)) [(a:as)]) = *code*
But this only gives me "Parse error in pattern: array". I cant see what's wrong?
You can only pattern-match on data constructors. array is not a data constructor; it is a regular function that internal uses the Array data constructor(s) to create and return an Array value. The internal details
of an Array are not exposed, preventing you from pattern-matching on them.
Instead, you need use the functions provided for looking at an Array value. These can be composed with a function that does take arguments you can pattern match on.
-- bounds :: Array i e -> (i, i)
-- elems :: Array i e -> [e]
showConfig :: Board -> String
showConfig (Board arr) = showConfig' (bounds arr) (elems arr)
where showConfig' :: ((Int,Int),(Int,Int)) -> [Life] -> String
showConfig' ((0,0),(w,h)) (a:as) = ...
If you modify your Board type to
newtype Board = Board { getArray :: Array (Int, Int) Life }
you can rewrite showConfig in an applicative style:
showConfig = (showConfig' <$> boards <*> elems) . getArray
where showConfig' ((0,0),(w,h)) (a:as) = ...
Arrayis a type constructor; what does its data constructor look like?arrayis a function that returns anArrayvalue, but it is not a data constructor.Data.Arraydoes not appear to export any data constructors, so you cannot do pattern matching on those values.