On Thursday, 27 October 2016 22:56:42 UTC+8, JHacks wrote:
>
> I have some confusion about how the function `comp` works, especially as
> compared to the threading macro `->>`.
>
> From the book *Clojure Programming* (pages 70-71 of Chapter 2: Functional
> Programming), the following two functions are described as functionally
> equivalent:
>
> (def camel->keyword
> (comp keyword
> str/join
> (partial interpose \-)
> (partial map str/lower-case)
> #(str/split % #"(?<=[a-z])(?=[A-Z])")))
>
> (defn camel->keyword*
> [s]
> (->> (str/split s #"(?<=[a-z])(?=[A-Z])")
> (map str/lower-case)
> (interpose \-)
> str/join
> keyword))
>
> Why does the first function, `camel->keyword`, need to use `partial` with
> the
> `map` and `interpose` functions? The second function, `camel->keyword*`,
> does
> not need to use `partial`.
>
I actually prefer the following style to both of the above:
(defn camel->keyword*
[s]
(let [words (str/split s #"(?<=[a-z])(?=[A-Z])")
lc-words (map str/lower-case words)
joined-words (str/join "-" lc-words)]
(keyword joined-words)))
Reasons:
- Your intermediate values are explicitly named, which helps to make the
code self-describing
- It is (marginally) more performant than the composed function case (I
think exactly matches the threading macro)
- You can use the intermediate values in more than one of the following
steps if needed, which can make refactoring / adding new features easier
- The ordering is (to me) more logical as it describes the stages of the
transformation in the order they are performed.
- It is less "Clever". Clever code is generally bad for maintenance and
future understanding. Both functional composition and the
code-transformation effects of the threading macro represent conceptual
overhead that you don't need to pay (in this case).
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