[Haskell-beginners] Randomly selecting a data constructor

[Yitzchak Gale]

Thomas Davie wrote:
> data FigType = TR1 | TR2 | TR3 | TR4 | SQ | L1 | L2 | Z1 | Z2 | Z3 | Z4 |
> NoFigure
>                deriving (Enum)
> randomFigure :: IO FigType
> randomFigure = toEnum <$> randomRIO (1,11)

You actually want randomRIO (0,10).

If you don't want to have to remember that, or to remember
to change "10" whenever the number of constructors changes,
you can use:

> data FigType = TR1 | TR2 | TR3 | TR4 | SQ | L1 | L2 | Z1 | Z2 | Z3 | Z4 |
> NoFigure
>                deriving (Enum, Bounded)
> randomFigure :: IO FigType
> randomFigure = toEnum <$>
>  randomRIO (fromEnum (minBound :: FigType), fromEnum maxBound)

Regards,
Yitz