Question

data Ray = Ray Vector Vector

or

type Ray = (Vector, Vector)

Which is preferred in idiomatic haskell? Why should I use one over the other?
I don’t care about performance.

It seems to make little difference with functions, e.g.:

trace :: Ray -> …

trace (Ray x d) = …
-- OR
trace (x, d) = …

Answer 1

The data version is preferred as it more clearly indicates the intent of the programmer — by creating a new type, you are pointing out to all that this is not merely a tuple, but a meaningful semantic entity, a Ray.

That then makes it possible to lean on the type system further, with custom instances for Ray, and optimizations not possible in tuples.