CODEWITHSUNDEEP
schemeracket
Dogo-San
Dogo-San

Reputation: 375

Is posible define a function (+= var amount) in racket?

I'm studying functional programming in racket, and a question test said:

In Java we can increment a varible using x += 10;

Can we define a function in Racket (+= var amount) with the same meanings of Java?

I'm not really sure, but I think no because I can't modify a variable with a function in racket.

Like:

(define myvar 10)

(+= myvar 1)

myvar

I'm keep getting 10, when I type myvar in the drracket console

Upvotes: 1

Views: 527

Answers (2)

Sylwester
Sylwester

Reputation: 48745

Basically x += 5 are short for x = x + 5 in most Algol languages. In Java I'm sure you cannot do what you are asking for. eg. 

public static void method plusEqual(int binding, int increment) {
  binding = binding + increment;
}

However in Scheme and Racket you can. Since the full form is (set! binding (+ binding argument)) I'm suggesting +set!

(define-syntax +set!
  (syntax-rules ()
    ((_ binding increment)
     (set! binding (+ binding increment)))))

(define test 10)
(+set! test 5)
test ; ==> 15

Upvotes: 4

river
river

Reputation: 1028

You cannot define a function to do this.

You can define a macro that expands to (set! var (+ var amount)) though, and that'll do it!

Upvotes: 1

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