On Fri, Aug 26, 2011 at 3:57 PM, Matthias Felleisen <matth...@ccs.neu.edu> wrote: >> 6. In reading the User's Guide, I was pretty surprised that first >> (unlike car) raises an error on a non-list. I eventually looked over >> at the Reference Guide where I learned that list? is O(1) and I was >> able to connect the dots -- "aha, now /this/ is a pretty cool reason >> to make cons cells immutable beyond the basic 'set-cdr! is nasty' ". >> I recommend the User's Guide include a comment or footnote that first >> is an O(1) operation -- you can just point to the Reference Guide for >> any details. > > Where do you think it's best to say so? Lists are a bit scattered > over the Guide, and I didn't find the place where (first '()) > signals an error. [Not that this is necessarily the best place.]
I agree things are a big scattered so it's not clear. first and rest are introduced in 2.3.2, but almost by accident and the section title wouldn't suggest this. first and rest are not mentioned in 3.8 which is certainly odd. So you might consider adding to 3.8 a paragraph on first and rest, how they're basically defined in terms of list?, car, and cdr (unless you'd prefer not to explain them that way -- I'm fine either way), and how list?, first, and rest are O(1) operations (again this could be in a sidebar). --Dan _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
