Additional Direction Instances

[ischeinfeld]

Would it make sense to derive Ord, Enum, and Bounded instances for Direction g? I am working on a game that should work in any grid and it seems to me that "turning left," for example, is well defined in all grids and could be defined in terms of Enum and Bounded. Or perhaps some other functionality could be added for iterating through directions, maybe with a different type class?

[mhwombat]

Thank you for the suggestion! Sounds like a good idea. I'll look into it.

[ischeinfeld]

Nice! I've been working with a local copy where I simply derive them for each internal Direction type. But maybe a custom type class, i.e. Rotate, would make more sense semantically?

Also, I'm not sure if there is some way to make the Grid class enforce these (and other, such as Eq) constraints on the Index and Direction types? I've been writing code that works on arbitrary grids and my type signatures include constraints like

Grid g, Eq (Index g), Eq (Direction g), Enum (Direction g), Bounded (Direction g)

where it would be great to just write Grid g, since I don't see a case where, for example, indices and directions wouldn't be comparable or directions wouldn't be rotatable. I'm still learning Haskell though so maybe there is already a way around this?