Hi, Am 28.02.2009 um 04:14 schrieb Mark Engelberg:
I expect: (rest [1]) -> () (rest []) -> nil Just as (first []) yields nil, so should (rest []), IMO.
The definition of rest, is that it returns a collection of items of the rest of the given seqable thing. first is a different case. It takes a seqable thing and returns a thing or nothing. If the given collection is empty (or it is given nil as a "sequence"), there is no first thing. Hence first returns nothing (nil). next is again different. It takes a seqable thing, and returns a sequence of the remaining items in the sequence without the first one or nothing if there are no more items (or there were none to begin with). rest is now a special view on the return value of next. It always returns a collection of the remaining items. If there are none, ie. next returned nil, this is the empty list, which is the concrete collection containing no items corresponding to an "empty sequence". So far everything seems consistent to me. rest is really just a different view of next. One can be considered the abstract concept, while the other is a concrete thing. Sincerely Meikel
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