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Scheme-Beginner: Why is inital undefined?

Scheme-Beginner: Why is inital undefined?

(OP)
Hello,

I do not understand the following problem. Here is a script from a learners book:

(define the-empty-stream '())
(define (cons-stream e s) (cons e s))
(define (head s) (car s))
(define (tail s) (cdr s))
(define (empty-stream? s) (null? s))

(define (right-reduce combine inital s)
(if (empty-stream? s)
initial
(combine (head s)
(right-reduce combine initial (tail s)))))

(define (sum s) (right-reduce + 0 s))

-------------
Now, when i am entering
(sum '(1 5))

the answer is:
initial: undefined;
cannot reference undefined identifier

and the "else-part" from the funciton right-reduce (combine (head s) ... is marked).

Can you tell me, what there is wrong? I cannot find an answer in the book. The author says, it works this way.

Thank you very much.

Christian

RE: Scheme-Beginner: Why is inital undefined?

(OP)
Oh, I am very sorry about this. Now I have found what the Problem is - after two senseless hours:
On the parameter of right-reduce I used "inital" (where I forgot an i after the t).

Is there a possibility to find those errors easier? I use DrRacket.

Best wishes,

Christian

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