# [BULK] Re: [plt-scheme] Re: HTDP - evidently not for everyone.

On Feb 12, 2010, at 7:10 AM, Noel Welsh <noelwelsh at gmail.com> wrote:
>* my suggestion is to drill the heck out of them. If you show them
*>* how to add up the elements of a list, can they then
*>* multiply/divide/subtract the elements of a list?
*
That's actually a trickier generalization than it looks, because it's
not obvious what the right answer to the empty case should be. Many
students are convinced (although they wouldn't phrase it this way)
that the right answer to any numeric-valued question about the empty
list is 0, and the answer to any Boolean-valued function on the empty
list is false.
>* Can they then
*>* string-append the elements of a list of strings?
*
This one is a better next step, because students' intuitive guess at
the answer to the empty case happens to be right.
My textbook makes a point of giving, for each topic, a "worked
exercise" followed immediately by an unworked exercise that's almost
identical, then one that's a little more different, and so on.
Steve