clojure - 为什么这个部分不起作用

Question

这是我的代码:

(def partial-join (partial (clojure.string/join ",")))

=>(clojure.string/join "," ["foo" "bar"])
"foo,bar"

=> (partial-join ["foo" "bar"])

它引发了这个异常:

ClassCastException java.lang.String cannot be cast to clojure.lang.IFn .repl/eval12557 (form-init2162333644921704923.clj:1)

Answer 1

请参阅 clojure.string/join 的文档。

clojure.string/join
([coll] [separator coll])
  Returns a string of all elements in coll, as returned by (seq coll),
   separated by an optional separator.

当clojure.string/join只提供一个参数时，该函数将其参数视为集合，因此:

user=> (clojure.string/join ",")
","

接下来，请参阅partial的文档。

clojure.core/partial
([f] [f arg1] [f arg1 arg2] [f arg1 arg2 arg3] [f arg1 arg2 arg3 & more])
  Takes a function f and fewer than the normal arguments to f, and
  returns a fn that takes a variable number of additional args. When
  called, the returned function calls f with args + additional args.

当仅提供一个参数时，partial 返回其参数。

user=> (partial (clojure.string/join ",")) 
","

试试这个:

user=> (def partial-join (partial clojure.string/join ","))
#'user/partial-join
user=> (partial-join ["a" "b"])
"a,b"