Clojure higher order functions

Question

I was solving problems in 4clojure and got stuck at Problem 46 or example

(= true ((__ >) 7 8))

where we need to fill in the _

Basically I need to create a function that would take in another function as an argument but don't know where to go with that. Also, the evaluation kind of confuses me, if I create an anonymous function

(fn [f] ())

which takes in the function > I don't know how to pass in the other arguments for > to operate on.

I don't want the answer, just some direction.

A couple tips: with a function f, you can do (apply f args) where args is a list, or (f arg1 arg2 ...). — Diego Basch
– Diego Basch, Commented May 30, 2014 at 18:36

stonemetal · Accepted Answer · 2014-05-30 18:46:54Z

5

Given what ever you put in the blank will take > and then be evaluated as a function what you need is a function that returns a function.

You have this:

 (fn [f] ())

How do we get that to return a function?

 (fn [f] (fn [something here] (something here)))

Now all you have to do is fill out the 'something here's.

answered May 30, 2014 at 18:46

stonemetal

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2 Comments

noMAD Over a year ago

Solved it (fn [f] (fn [a b] (f b a))) The returning a function part was a bit confusing initially. Thanks!!

edbond Over a year ago

nice, you can also use complement and partial - ((complement (partial >)) 7 8)

Gosha A · Accepted Answer · 2014-05-30 18:55:56Z

0

The function you are looking for is the one that returns a function that reverses its arguments and applies to the original function:

(fn [f]
  (fn [x y]
    (f y x)))

edited May 30, 2014 at 18:55

answered May 30, 2014 at 18:49

Gosha A

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1 Comment

stonemetal Over a year ago

If you click through to the actual problem set he is looking at, that is not right. What they are looking for is a swap the arguments to the given function. One of the other examples is (= 3 ((__ nth) 2 [1 2 3 4 5]))

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