The comparison of Shen and Haskell caught my eye since Shen was mentioned in HN a few days ago, and I was looking into it. Since I've used Scheme and a port of Shen runs under Chibi Scheme, I wondered what error would show up in Scheme. If I manage to get Shen working (under Chibi) it will be even more interesting to see what it does.

Translating, the original problem was:

    (if (null? xs) (cdr xs) xs)

So:

    (define (mytl xs) (if (null? xs) (cdr xs) xs))

And:

    (mytl '())
    Error: (cdr) bad argument type: ()

It appears (mytl) emits a type error in this instance.

This is obviously a run-time error, and without specific effort I don't think it would be known at compile-time in the Scheme implementations I'm familiar with.

Since the Scheme expression appears to embody the semantics of the original problem, I'm inclined to think it shows an underlying difference in the handling of the null list between CL and Scheme implementation I used.

If I'm completely wrong, and I can't rule out that possibility, I hope someone will point in the right direction.