[Haskell-cafe] Void vs ()

[MarLinn]

> My question is then: What's the best thing to use for "x", Void or ()?
> […]
> An alernative I've been considering is actually to create a Foo' type 
> which actually does eliminate the i parameter 

This is only a partial answer, but why not role your own i? And why not 
define Foo' in terms of Foo and whatever you end up using?

data ThereIsNoIOnlyZuul    -- intentionally left blank

type Foo' e n = Foo ThereIsNoIOnlyZuul e n    -- extra types included for clarity

The reason I suggest this is that a) your own types are also 
documentation and b) you can change the behavior of your new type at will.

Speaking of new types…

> (Aside: AFAICT there's no reasonable way to implement anything like 
> Foldable or Traversable to avoid the explicit "toList" function, 
> right? […])
I suspect the canonical answer would be to use copious amounts of 
newtype. Downside: lots of wrapping and unwrapping. Upside: it's like an 
early Christmas!

Cheers,
MarLinn