Hi all, I'm new to the group; I have some experience with both CL and
Java, though it's been a while for each. Anyway I really like Clojure
as a way of combining the best parts of the two languages, but I'm
still getting the hang of it and there are often things that confuse
me.
For example, I wanted to define a ring function, which takes as input
N objects, and returns a hash table mapping object N to object N+1
(mod N). I intended to use this to describe a compass object:
(ring :w :n :e :s) should result in {:w :n, :n :e, :e :s, :s :w}.
I could have done this with basic recursion or as a list comprehension
using (for), (count), and (rem), but it seemed there must be a more
elegant solution with lazy sequences, like maybe combining cycle and
map to gloss over the N==0 wraparound issue. What I came up with was
frankly a monstrosity; I don't have the source with me at work, but it
looked roughly like:
(defn ring [& elts]
(apply assoc {}
(map #(list
%1
(fnext (drop-while
(comp (partial or
(partial not= %1)
nil))
(cycle elts))
elts))))
Since then I've realized I could have used nth and map-indexed to get
a less ugly result, but I was baffled by the awkwardness of drop-
while: is there a reason it demands nil or not-nil, instead of
treating false and nil as logical false? Converting false to nil was a
real bear (and retyping this from memory I'm pretty sure my syntax for
comp/partial/or is wrong somewhere), and in my experience clojure is
too clever make me do crap like this; what am I missing?
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