scheme how to return a form symbol + *

Question

How can I define on scheme language this function that return if x>0 + else * like:

plus_or_muliti(int x) {
    if (x>0) return +;
    else return *;
}

i try this and it not work on racket:

(define (plus_or_multi x)
  (if (>= x 0) + *))

i got this error

+: expected a function call, but there is no open parenthesis before this function

That happens because of the language you're using, switch to a more advanced language in the options, or better yet, use `#lang racket` — Óscar López, Apr 04 '17 at 21:10
If your supposed to be using the teaching languages, don't use `#lang racket`, use Intermediate Student Language plus Lambda. — Alex Knauth, Apr 05 '17 at 00:40
You seem to have a typo on `plus_or_muliti` - there's an extra `i` in the middle, whereas you call `plus_or_multi`. — Máté, Apr 05 '17 at 06:28

score 0 · Answer 1 · answered Nov 02 '17 at 23:17

That code is perfectly valid in a full Scheme (in this case, Racket) implementation, but based on the error you're getting it looks like your using the Beginning Student Language, one of the several languages that the Racket system comes with. BSL is designed to help avoid some of the usual beginner mistakes when using Scheme-based languages, and all of the teaching-languages are designed to be used in tandem with the How to Design Programs book. In fact, a few libraries that come with Racket are in the htdp or htdp2 module, and derive from that book, even though they can be used for general purpose applications. In the DrRacket Language -> Choose Language menu, you can select the full version of the language, which will allow you to use the... full language.

score -2 · Answer 2 · answered Apr 05 '17 at 07:23

-2

Your code is fine.

$ chibi-scheme
> (define (plus_or_multi x)
(if (>= x 0) + *))
> (plus_or_multi 5)
#<opcode "+">
> (plus_or_multi -2)
#<opcode "*">

It is not a Scheme interpreter, what you are using.

answered Apr 05 '17 at 07:23

ceving

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Yaniv Valotker is using Beginning Student Language, a variant of Scheme/Racket that is restricted so that it can help with more beginner mistakes. – Alex Knauth Apr 05 '17 at 16:55
Instead of helping beginners it confuses beginners, because it breaks the simplicity of Scheme. Principles are Scheme's greatest strengths. And what ever Racket is trying to do here is counterproductive. – ceving Nov 08 '17 at 08:36

scheme how to return a form symbol + *

2 Answers2