On Wed, Nov 2, 2011 at 5:37 AM, Dennis Haupt <d.haup...@googlemail.com> wrote:
> i stumbled over two odd things
> 1) -> and ->> have the same source code. why is that?
-> and ->> are macros that have similar purposes. "->" inserts the previous form
as the first argument to the function, "->>" inserts it as the last.
> 2) why can't i use "(-> "hi" #(println %))" directly? why do i have to
> put my function into a symbol first? is there a way to avoid this?
This is one is a bit more involved. The #(func ...) form is a reader
macro so it gets
translated before macro expansion occurs:
user> (read-string
"(-> \"hi\" #(println %))")
(-> "hi" (fn* [p1__2134#] (println p1__2134#)))
The result is that your initial string is inserted into a lambda
expression in the wrong place (where the parameter list should be).
When clojure tries to compile the resulting form after macro
expansion, you get an error:
user> (macroexpand '(-> "hi" (fn* [p1__2134#] (println p1__2134#))))
(fn* "hi" [p1__2134#] (println p1__2134#))
####
The easiest fix if you need to use inline function definitions is to
wrap them in parens:
(-> "hi" (#(println %)))
Although, in this case it's not necessary, it would have been easier to do
(-> "hi" println)
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