[plt-scheme] HTDP 21.2

From: Don Blaheta (dblaheta at knox.edu)
Date: Tue Apr 10 16:51:46 EDT 2007

I'm either looking to report a few errata or curious to hear an
explanation.  In section 21.2 of HtDP (p 313 in the dead tree version),
a number of higher-order functions are listed as being defined in
Scheme, and by implication, in the language levels associated with the

One is (quicksort cmp alox), even in the most-updated online version;
but that function is listed in the library documentation as deprecated
in favour of (sort cmp alox).  Which isn't a huge problem, except that
the language-level Scheme doesn't seem to have sort defined.

Of somewhat greater concern is that (assf p? alop) is listed in this
figure, but is no longer present in any of the language levels.  A
couple of my students have hounded me about this; one of the problems I
had written was on an alist, and I'd explicitly pointed them at the
various alist functions (some, like assq, *are* defined).  I ended up
just telling them to write assf themselves as an exercise, but I'm
wondering why it got taken out (if indeed that was even intentional)....

-=-Don Blaheta-=-dblaheta at knox.edu-=-=-<http://faculty.knox.edu/dblaheta/>-=-
"The path to wisdom is through discipline, and the path to intelligence
through carefully selected self-indulgence."	--Paul Graham

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