On Jun 30, 2010, at 5:44 AM, Horace Dynamite wrote:
Hi Barry,
I noticed that beginning students are able to use list abbreviation
constructors. It doesn't return the list in abbreviated form,
however.
(list 1 2 3)
returns
(cons 1 (cons 2 (cons 3 empty)))
Is that correct?
Yes. It accommodates people who use the Little books with the teaching
languages. (I used to have a language collection for TLL/S, but I
failed to maintain it.) Also see (define f (lambda (x) x)).
I've noticed some overlaps of functionality between the teaching
languages myself too. I remember using this feature when I first
encountered the list abbreviations though, since for a while I wasn't
confident what a nested (list ... (list ...)) might look like in the
cons form.
As a side note, a lot of people have trouble with the arrangements
exercise in section 12, which is a little cleaner to work with using
list abbreviations, so thats another possible reason for including
this functionality in the beginning student language.
I am in the process of working this extended exercise into HtDP/2e
AFTER introducing (list "h" "e" "l" "l").
-- Matthias
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