Achieving variables in the local syntax in the Scheme environment

Question

How we can achieve variables that we defined in the (local ...) syntax in Scheme? For example in this code below,

(define (erkan x)
   (local 
      ((define y 10))
      (* x y)))

how can I directly get the value of y ?

Answer 1

You are accessing y when you're doing (* x y).

If you want to access y from outside of the local-block: you can't do that. Any definitions made inside a local-block are local to that block and cannot be accessed from outside.

Answer 2

Either this is a strange question, or you didn't phrase it right... Your sample code uses y, so it does have access to it. Maybe you're trying to get just the value of y:

(define (erkan x) (local [(define y 10)] y))

Or maybe you want to create a kind of an "object thing" -- this is possible, but involves more advanced code. Here's a quick example just to show you how it's done, (but if you're going through HtDP, you're better off leaving this for later).

(define (erkan x)
  (local [(define y 10)
          (define (handler message)
            (cond
              [(eq? message 'get-x) x]
              [(eq? message 'get-y) y]
              [(eq? message 'compute) (* x y)]
              [else (error "bad message")]))]
    handler))
(define some-erkan (erkan 3))
(some-erkan 'get-x)
(some-erkan 'get-y)
(some-erkan 'compute)

(Note BTW that this is not proper Scheme, but the teaching student dialects used in HtDP.)