stupid adt example

stupid.hs

module Scratch where

data Shape = Circle { radius :: Int }
  | Rectangle {length :: Int, width :: Int}
  | Triangle {length :: Int, height :: Int}
  deriving (Show, Eq)


-- how would you fromJSON shape assuming there
-- was no tag on the json

-- e.g.

-- {"radius": 1 } <- a circle
-- {"length": 1, "width": 1} <- a rectangle
-- {"length": 1, "height": 2} <- a triangle

-- none of the JSON are tagged with what shape
-- they are
-- e..g there is no {"tag": "Circle", "radius": 1}
-- I could have a complicated ToJSON method
--  and start looking for keys?

-- does making an intermediate wire format type
-- for Shape that holds all possible shapes work?

data UrShape = UrShape {
    radius_ :: Maybe Int
  , length_ :: Maybe Int
  , width_ :: Maybe Int
  , height_ :: Maybe Int
                       }

instance FromJSON UrShape ...

-- and a bunch of

asCircle :: UrShape -> Maybe Circle
asRectnalge :: UrShape -> Maybe Rectangle
asTriangle :: UrShape -> MaybeTriangle

-- and some parser that is uhh
-- asCircle <|> asRectangle <|> asTriangle
--?