How come the following compiles fine:

Void process2(|Int -> Void |[] functions)
{
  functions.each | | Int -> Void| fun, Int index |
  {
    fun(0)
  }
}

but if I change the return type of the closure to Void, the compiler complains:

Void process(|Void -> Void |[] functions)
{
  functions.each | | Void -> Void| fun, Int index |
  {
    fun()
  }
}

The error corresponds to the fun() invocation:

/Users/cbeust/fan/curry.fan(30,7): Invalid args |sys::Void|, not ()

-- Cedric

Like method signatures, you only use Void for return. Unlike methods, you can omit the Void return (it is optional):

|Void -> Void| fun  // illegal just like Void m(Void) would be
|->Void| fun        // ok
|,| fun             // shortcut for above
|Int->Void| fun     // ok
|Int| fun           // shortcut for above

Can I count these questions as evidence that it's confusing when methods put the return type on the left but function types and closures put the return type on the right?

No