All you have to do is abstract the function you want (by 'abstract' I
mean "put it in the argument list and replace the function with the
variable"):
(defn sum2 [func incr a b]
(if (> a b)
0
(+ (fn a) (sum2 func incr (incr a) b))))
You wouldn't want to use this code in the real world since it involves
non-tail recursion----something more idiomatic would be like this:
(defn sum3 [func incr a b]
(if (> a b)
0
(reduce + (map func (take-while #(<= % b) (iterate incr a))))))
I admit this is not as elegant-looking; recursive functions are nearly
always more elegant! Note I've used the short form for anonymous
functions; I could have written (fn[x] (<= x 3)) instead, but the
short form is preferable for inline functions. (You need to rename
your function var to something other than 'fn', since that is a
Clojure keyword.)
On Oct 30, 6:48 pm, Aquahappy <[email protected]> wrote:
> Hi All,
>
> I'm watching Brian Harvey's SICP lecture #3 from Berkeley 61A/Spring
> 2011 and had a question about how I could refactor the following
> function so that the (+a 1) can be abstracted to be a function and
> passed in.
>
> Here is the original:
>
> (defn square [x] (* x x))
>
> (defn sum [fn a b]
> (if (> a b)
> 0
> (+ (fn a) (sum fn (+ a 1) b))))
>
> => (sum square 2 4)
> 29
>
> That works. So then I want to replace (+ a 1) with a function like:
>
> (defn addone [a] (inc a))
>
> but I'm not sure how this would be structured.
>
> I'm new to clojure and realize this is a stepping stone to learning
> about higher order functions so apologies in advance for any code
> ugliness due to my newness to clojure.
>
> Thanks for your help!!!
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