Comp does its work at run-time, so you have to call functions that return
functions. Threading macros do their work at compile-time, so your form
literally compiles to this:
> (clojure.walk/macroexpand-all '(->> (str/split s #"(?<=[a-z])(?=[A-Z])")
(map str/lower-case)
(interpose \-)
str/join
keyword))
(keyword
(str/join
(interpose \-
(map str/lower-case
(str/split s #"(?<=[a-z])(?=[A-Z])")))))
On Thu, Oct 27, 2016 at 10:56 AM JHacks <[email protected]> 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`.
>
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