esgab26 (esgab26) wrote in lisp,

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Can any one help?-About the "cond" operator ----(novice)

Hi everyone,

I've read this in SICP book from MIT-OCW:

"A minor difference between if and cond is that the <e> part of each cond clause may be a sequence of expressions. If the corresponding <p> is found to be true, the expressions <e> are evaluated in sequence and the value of the final expression in the sequence is returned as the value of the cond. In an if expression, however, the <consequent> and <alternative> must be single expressions. "

so i tried this in scheme:

(define (test a b)
    (cond ((> a b) ((- a 1) (- b 1)))
               ((< a b) ((+ a 1) (+ b 1)))
               (else((+ a b) (- a b)))))

(test 3 2)

it returned: procedure application: expected procedure, given: 2; arguments were: 0

What I'm trying to do is: given a single predicate, evaluate multiple expressions (like the ones above, evaluate both (- a 1) and (- b 1)

i thought this is possible: (because of what i've read- or maybe i just don't understand it)

(cond <predicate> (<exp1> <exp2> <exp3>))- but it always result in an error

Can some one help me with this? What is meant by sequence of expressions?

Thank you very much


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