How Can i construct correct String in Clojure?

Question

I am newbie in Clojure. I have following Expressions:

(= (__ "Dave") "Hello, Dave!")

(= (__ "Jenn") "Hello, Jenn!")

(= (__ "Rhea") "Hello, Rhea!")

In place of __, in all 3 places must be inserted same expression so that the equality check in all 3 cases are true. At this point i have come up with str "Hello, ". As i understand this should produce "Hello, Dave" "Hello, Jenn" "Hello, Rhea" How do i put "!" mark at the and of each string? (I can only "write" expression in place of __)

Thank you

Not so interesting answer is (= (format "Hello, %s!" "Dave") "Hello, Dave!"). but I don't know this is expected one. — ymonad
– ymonad, Commented Sep 13, 2019 at 6:44
@ymonad Thank you for the reply. I will have look at function format. But it certainly returns expected values — Tornike Shavishvili
– Tornike Shavishvili, Commented Sep 13, 2019 at 6:48
(= (str "Hello, " "Dave" "!") "Hello, Dave!") will work just fine as well :) — Jonas Johansson
– Jonas Johansson, Commented Sep 13, 2019 at 7:27
@JonasJohansson It certainly would work but only for the first problem (Dave) for others (Jenn, Rhea) it would not work. The idea is that it should work for all three — Tornike Shavishvili
– Tornike Shavishvili, Commented Sep 13, 2019 at 7:35
I see. Yeah, then make it a funcion like (fn [name] (str "Hello, " name "!")) or similar ;) But I see that there is a perfectly good answer below now. Happy Clojuring! — Jonas Johansson
– Jonas Johansson, Commented Sep 13, 2019 at 7:37

David Tonhofer · Accepted Answer · 2019-09-13 07:23:47Z

5

You want to drop a function into the place of __.

This function shall take a string s and shall return a string that is based on s so as to satisfy the three test cases.

A possible function is

(fn [s] (str "Hello, " s "!"))

which can written using Clojure syntactic sugar

#(str "Hello, " % "!"))

Thus

(= (#(str "Hello, " % "!") "Dave") "Hello, Dave!")

Bonus: Using testing framework

Clojure comes with a nice testing library, clojure.test (I don't know why it is called an API, which would mean there is a component on the other side of the callable functions; it's just a library)

We can use the testing library for good effect:

(require '[clojure.test :as t]) ; make library visible

(def myfun (fn [s] (str "Hello, " s "!"))) ; our function as symbol myfun

(t/deftest test-stringmanip
   (t/is (= (myfun "Dave") "Hello, Dave!"))
   (t/is (= (myfun "Jenn") "Hello, Jenn!"))
   (t/is (= (myfun "Rhea") "Hello, Rhea!")))

(t/run-tests) ; do it!

edited Sep 13, 2019 at 7:23

answered Sep 13, 2019 at 7:09

David Tonhofer

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1 Comment

amalloy Over a year ago

API stands for Application Programming Interface. It is the interface you are meant to program against when using a component, such as a testing library. There's no implication that it's a client/server protocol.

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