I'm very new to continuation passing style (CPS), and as part of the
learning process I've done a CPS version of a "flatten" function. Ie, it
does the same thing as the standard clojure "flatten", but is implemented
using a recursive local CPS helper function. I'm interested in comments /
critiques on what I've done.
Here it is...
(defn my-flatten
[xs]
(letfn [(my-flatten-cps [xs k]
(if (nil? xs)
(k '())
(let [x (first xs), ys (next xs)]
(if (sequential? x)
(recur ys (fn [v] (my-flatten-cps (seq x) (fn [w] (k
(concat w v))))))
(recur ys (fn [v] (k (conj v x))))))))]
(my-flatten-cps (seq xs) identity)))
I'm relatively inexperienced with clojure, so please feel free to suggest
improvements to my clojure code.
But what I'm most interested in is understanding CPS better and about how
it interacts with Clojure and with "recur". As you can see, my-flatten-cps
uses recur nicely to traverse at a breadth level. But as we sink down into
depth, I've done an actual non-recur call to my-flatten-cps. I presume I
can't do a recur here instead (because it would attempt to jump to the most
immediate fn??) - is this correct?
Is there any way around this? (As I write this, the word "trampoline"
comes to mind - some videos I've watched speak of this - but not sure how
this would work and what efficiency trade-offs would be involved.)
The other things is... is it so bad that it is not fully using recur -
maybe using a bit of stack is okay??
Thanks,
Mark.
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