在Haskell中创建数据类型

Question

I would like to create a new data type that either takes in Start or A tuple of values. This is what I have:

type Coord = (Int, Int)
data Direction = N | E | S | W
                 deriving (Eq, Show, Read)


type Move = (Coord, Direction)
type BoardSpec = [(Coord, Bool)]

type GameTreeNode = (GameTree2, BoardSpec, Move)
data GameTree2 = Start | GameTreeNode deriving(Show)


blahblah :: GameTree2
blahblah = blahb

blahb :: GameTreeNode
blahb = (Start, testbo, ((1, 1), N))

This however, gives me the error on blahblah

Couldn't match type `(GameTree2, Move)' with `GameTree2'
Expected type: GameTree2
  Actual type: GameTreeNode

Answer 1

data GameTree2 = Start | GameTreeNode deriving(Show)

expands to:

 
 
 
  
  data GameTree2 = Start | (GameTree2, BoardSpec, Move) deriving(Show)
 
  

You can't make a tuple a valid value of your type.

---

You need to wrap it in a constructor:

 data GameTree2 = Start | Node GameTreeNode deriving(Show) 

where Node is whatever name you choose for it.