[Haskell-beginners] Dipping Toes Into Haskell

[Timothy Washington]

To get started, I'm trying to implement a simple *tictactoe* game. And I
would like to be able to represent a Piece on the board, as either the
string "X" or "O". This is what I have so far.

module Main where

data Piece = X | O
type Row = [Piece]
type Board = [Row]

-- put an X or O in a position
move :: Board -> Piece -> Board
move board piece = board

-- check win vertically
-- check win horizontally
-- check win diagonally

main :: IO ()
main = putStrLn "Hello World"



*A)* Now, I'd like to be able to *load code interactively*, preferably
within emacs. However I don't have access to my types with *ghci* or *ghc-mod
(Interactive-Haskell)*. In either case, this call fails with the below
error.


let p = Piece X
<interactive>:20:9-13: Not in scope: data constructor `Piece'


*B)* And how do I make a *custom datatype* that's one of two strings
(enumeration of either "X" or "O"). Cabal builds and runs the abouve code,
so I know it can compile. But I'm confused as to where X or O is defined,
and how I would supply it as an input.

*C)* Finally, how do we update nested lists in Haskell. I want the move
function to take a Board, Piece, and Position, and return a Board. I see
some results from Hoogle <https://www.haskell.org/hoogle/?hoogle=update>.
Is this where Lenses <https://www.haskell.org/hoogle/?hoogle=lens> or
Zippers <https://www.haskell.org/hoogle/?hoogle=zipper> come into play?


Thanks

Tim Washington
Interruptsoftware.com <http://interruptsoftware.com>
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