Move parameter in Clojure function

Question

I'm working on 4clojure problem 29 : "Get the Caps" ``` (= (__ "HeLlO, WoRlD!") "HLOWRD") ``` I've written a solution in the REPL: ``` user=> (apply str (filter (fn [foo] (some #(= % foo) (map char (range 65 91)))) "AbC")) "AC" ``` But as you can see my parameter "AbC" is nested two parentheses in. How would I move my parameter to the outside so I can use it in the 4clojure test? Have I approached the problem in the wrong way?

Accepted Answer

You don't need to move the a parameter to the outside, you can just use the same technique you used to create the filtering function, that is, with `fn`:

```
(fn [string] 
  (apply str 
    (filter 
      (fn [foo] (some #(= % foo) (map char (range 65 91)))) 
      string)))
```

As an example of this, the following two statements are the same:

```
(+ 1 2 3)
((fn [n] (+ 1 2 n)) 3)
```

However, to actually answer your question, you could use `comp` ("compose") and `partial` to move the parameter to allow eta conversion (that is the technical name for the last part of the manipulation you are attempting to do):

```
(comp (partial apply str)
      (partial filter (fn [foo] (some #(= % foo) 
                                       (map char (range 65 91))))))
```

This expression is now a function that takes a string, filters the capital letters and then converts it back to a string (notices that `comp` applies functions from right to left).

(NB, that last expression probably isn't very idiomatic Clojure; the first method, or one of the suggestions of others, is better.)

Move parameter in Clojure function

Solution

Problem