[plt-scheme] Implementing constructors for environment interface

> #lang scheme
>
> (require htdp/testing)
>
> (define (extend-env* vars vals f)
>   (lambda (var)
>     (if (member var vars)
>         (foldl (lambda (var* val* r) (if (eq? var* var) val* r))  
> (gensym) vars vals)
>         (f var))))
>
> (define new-stack (extend-env* '(var1 vark) '(val1 valk) (lambda  
> (x) 10)))
>
> (check-expect (new-stack 'var1) 'val1)
> (check-expect (new-stack 'vark) 'valk)
> (check-expect (new-stack 'x) 10)
>
> (test)




On Feb 10, 2009, at 9:10 AM, aditya shukla wrote:

> I have an interface , how can i implement a constructor extend-env*  
> using a list representation such that
>
> (extend-env* (var1 ... vark) (val1 ... valk)  f ) = g,
>
> where g(var) =vali if var = vari for some i such that 1 ² i ² k
> f (var) otherwise
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