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Weird error.

Weird error.

Weird error.


CODE --> Scheme

(define (sum-alt term a next b) ((cond
                                   [(> a b) 0]
                                   ((even? (+ a 1)) (+ (term a) (sum-alt term (next a) next b) ))
                                   [else (+ (- (term a)) (sum-alt term (next a) next b))])))) 

this is my code.
I'm trying to run sum-alt with :

CODE --> scheme

(sum-alt (lambda(x) x) 1 (lambda(x) (+ x 1)) 3) 

but I'm getting:

CODE --> scheme

application: not a procedure;
 expected a procedure that can be applied to arguments
  given: 0
  arguments...: [none] 

I'm really frustrated. I've no idea what is wrong with this code.
Could you guys tell me what im doing wrong?

Thank you !

RE: Weird error.

There is an unnecessary bracket before cond :

CODE --> Scheme

(define (sum-alt term a next b) (cond
                                   [(> a b) 0]
                                   ((even? (+ a 1)) (+ (term a) (sum-alt term (next a) next b) ))
                                   [else (+ (- (term a)) (sum-alt term (next a) next b))]))) 

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