Question

If I do the following:

user=> (-> ["1" "2"] (partial apply str)) 
#<core$partial__5034$fn__5040 clojure.core$partial__5034$fn__5040@d4dd758>

…I get a partial function back. However, if I bind it to a variable:

user=> (def apply-str (partial apply str))
#'user/apply-str
user=> (-> ["1" "2" "3"] apply-str)       
"123"

…the code works as I intended it. I would assume that they are the same thing, but apparently that isn’t the case. Can someone explain why this is to me?

Answer 1

-> is a macro, so it doesn’t have to follow the rules you would expect in terms of application. The macro transforms the source before the forms are evaluated. Try macroexpanding the forms:

user> (macroexpand '(-> ["1" "2"] (partial apply str)))
(partial ["1" "2"] apply str)

What are you trying to achieve here by using the ‘->’ macro?

EDIT: Note that:

user> ((partial apply str) ["1" "2"])
"12"